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Get the fix to "<strong>0xc0000021A: </strong>error for<strong> Windows XP, Vista, 7, 8, </strong><strong>8.1</strong>, <strong>10</strong> or <b>Windows 11</b> operating systems.

<h2>About the "<strong>0xc000021A</strong>" error</h2>

[kbintro]
<h3>Description and Symptoms</h3>
The error messages, alerts, warnings, and symptoms below are tied to this error.
<h4>Symptom 1: 0xc000021A error screen</h4>
The 0xC000021A error is a Blue Screen of Death or BSoD error (related: <a href="https://neosmart.net/wiki/blue-screen-of-death/">Blue Screen of Death guide</a>) that occurs when a Windows user-mode subsystem is compromised.
<h3>Description</h3>
Windows user-mode subsystems are: WinLogon or Client Server-Run Time Subsystem (CSRSS). These 2 sub-systems are mandatory for Windows to operate.

If these are compromised, Windows stops running and will show this error.

The error message that can appear on your screen is usually this:
<pre>STOP: c000021a {Fatal System Error}
The Windows SubSystem system process terminated unexpectedly with a status of 0xc0000005.
The system has been shut down.</pre>
The 0xC000021A error is also known as:
<ul>
 	<li>STOP 0xC000021A</li>
 	<li>STATUS_SYSTEM_PROCESS_TERMINATED (Status System Process Terminated)</li>
 	<li>HALT: c000021a {Fatal System Error}</li>
 	<li>STOP c000021a</li>
</ul>
This is how 0xC000021A appears on a Windows XP system (also for Windows Vista or Windows 7 systems):

Under Windows 8, Windows 8.1, Windows 10, and Windows 11, the blue screen and error message would appear as a variation of the following screenshot. The text might differ slightly, but with the same error code:

<h3>Causes of this Error</h3>
This error has been known to occur as a result of one or more of the following:
<h4>Cause 1: Misconfigured software or driver</h4>
The most common cause of this error is a certain key piece of software or system driver that is malfuncioning.
<h4>Cause 2: System registry is damaged</h4>
Another possible cause for this error is damaged system registry. This may happen because of disk read/write errors, power outages or virus attacks.
<h2>Fixing "0xc000021A" on Windows</h2>
[easyre error="0xC000021A" bootscreen="xp-vista-7-8-10" guaranteed="true"]
<h2>Fix 0xC000021A on Windows XP</h2>
<h3>Fix #1: Boot into Last Known Good Configuration</h3>
If you boot your Windows XP system into the Last Known Good Configuration mode, it forces your computer to use a previously saved Windows Registry version: the last time when your computer successfully boot with no errors.

The Last Known Good Configuration mode might be a quick fix for the 0xC000021A error.

To boot your computer into this mode, follow these steps:
<ol>
 	<li>Restart the computer</li>
 	<li>Wait for the computer to complete the POST process (system information appearing on your screen)</li>
 	<li>Quickly press the <kbd>F8</kbd> key repeatedly until you see a list of boot options available</li>
 	<li>Choose <strong>Last Known Good Configuration (your most recent settings that worked)</strong></li>
 	<li>Press <kbd>Enter</kbd></li>
 	<li>Wait for your computer boot into this mode</li>
</ol>
[caption id="attachment_1964" align="alignnone" width="980"]<a href="https://neosmart.net/wiki/wp-content/uploads/sites/5/2014/05/windows-xp-advanced-options-screen.png"><img class="wp-image-1964 size-full" src="https://neosmart.net/wiki/wp-content/uploads/sites/5/2014/05/windows-xp-advanced-options-screen.png" alt="Windows XP Advanced Options Menu" width="980" height="500" /></a> Windows XP Advanced Options Menu[/caption]
<h3>Fix #2: Uninstall previously installed software or driver</h3>
If the error appeared recently after you installed a new piece of software or hardware driver, or any kind of new installation to your Windows XP system, boot into Safe Mode and uninstall it.

Contact the manufacturer or check online for an update version of that software or driver that is compatible with Windows XP.

To boot Windows XP into Safe Mode, follow these steps:
<p class="info">If you're not able to boot into Safe Mode, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a> to fix this error automatically using Easy Recovery Essentials. You can run EasyRE from any CD, DVD or USB drive.</p>

<ol>
 	<li>Reboot the computer</li>
 	<li>Press the <kbd>F8</kbd> key before the Windows XP logo appears</li>
 	<li>At the <em>Windows Advanced Options</em> menu, select <strong>Safe Mode</strong></li>
 	<li>Press <kbd>Enter</kbd></li>
</ol>
<img src="/wiki/wp-content/uploads/sites/5/2013/09/Windows-XP-Advanced-Boot-Options.png" />

For more information on Safe Mode, go to <a href="https://neosmart.net/wiki/safe-mode/">our guide on Safe Mode</a>.
<h3>Fix #3: Run System Restore</h3>
If System Restore was turned on for your computer, you can try and restore the system to an earlier restore point.

To do so, follow these steps to run System Restore in Safe Mode on a Windows XP system:
<ol>
 	<li>Restart the computer</li>
 	<li>Press and <kbd>F8</kbd> key to boot into <strong>Windows Advanced Options</strong> Menu</li>
 	<li>Using the arrow keys, select <strong>Safe mode with Command Prompt</strong></li>
 	<li>Hit <kbd>Enter</kbd></li>
 	<li>Login as Administrator</li>
 	<li>When Command Prompt Appears, type the following command and press <kbd>Enter</kbd>:
<pre>%systemroot%\system32\restore\rstrui.exe</pre>
</li>
 	<li>Follow the instructions on the screen to restore your computer to an earlier time</li>
</ol>
[caption id="attachment_1964" align="alignnone" width="980"]<a href="https://neosmart.net/wiki/wp-content/uploads/sites/5/2014/05/windows-xp-advanced-options-screen.png"><img class="wp-image-1964 size-full" src="/wiki/wp-content/uploads/sites/5/2014/05/windows-xp-advanced-options-screen.png" alt="Windows XP Advanced Options Menu" width="980" height="500" /></a> Windows XP Advanced Options Menu[/caption]

For more information on System Restore, go to <a href="https://neosmart.net/wiki/windows-system-restore/#Restore_Windows_XP">our guide on System Restore for Windows XP</a>.
<h3>Fix #4: Other tips</h3>
If none of the above tips are working for your computer, consider the following tips you can try:
<ul>
 	<li>Reinstall Windows XP using the original installation disc. If you don't have the original disc, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a>.</li>
 	<li>Install all the Service Packs available for your Windows XP. If you have Windows XP with no Service Packs, install them.</li>
</ul>
<h2>Fix 0xC000021A on Windows Vista and 7</h2>
<h3>Fix #1: Uninstall previously installed software or driver</h3>
If you recently installed a new software or driver on your system, boot into Safe Mode and uninstall it.
<ol>
 	<li>Restart the computer and press the <kbd>F8</kbd> key before the Windows Vista or Windows 7 logo appears</li>
 	<li>At the <em>Advanced Boot Options</em> menu, select <strong>Safe Mode</strong> and press <strong>Enter</strong></li>
</ol>
<h3>Fix #2: Use Startup Repair</h3>
Your original Windows Vista or Windows 7 installation disc (DVD) contains the Startup Repair utility that you can run and try to fix the 0xC000021A error.

To run Startup Repair on a Windows Vista or 7 system, follow these steps:
<ol>
 	<li>Boot from the DVD, the original DVD with Windows Vista or 7
<p class="info">If you don't have the original DVD, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a>. EasyRE can automatically fix this error.</p>
</li>
 	<li>Click any key to boot from the DVD</li>
 	<li>At the <em>Welcome</em> screen, click <strong>Repair your computer</strong>The Welcome screen in Windows Vista:<img src="/wiki/wp-content/uploads/sites/5/2014/06/windows-vista-repair-your-computer.png" />The Welcome screen in Windows 7:<img src="/wiki/wp-content/uploads/sites/5/2013/10/Install-Now-Windows-7-300x225.jpg" /></li>
 	<li>Choose your operating system</li>
 	<li>Click <strong>Next</strong></li>
 	<li>At the System Recovery Options screen, click <strong>Startup Repair</strong>The System Recovery Options screen on a Windows Vista:<img src="/wiki/wp-content/uploads/sites/5/2014/06/windows-vista-system-recovery-options.jpg" />The System Recovery Options on a Windows 7:<img src="/wiki/wp-content/uploads/sites/5/2013/08/System-Recovery-Options-300x223.png" /></li>
 	<li>Wait for the process to finish</li>
 	<li>Restart the computer when prompted</li>
</ol>
<h3>Fix #3: Last Known Good Configuration</h3>
Similar to Windows XP instructions above, you can also try to boot into the Last Known Good Configuration that will attempt to use a previously error-free version of your system's Registry.

To boot into this mode on a Windows Vista or Windows 7 system, follow these steps:
<ol>
 	<li>Restart your computer or shut it down completely and then press the power button to start it</li>
 	<li>Before the Windows Vista or Windows 7 logo appears on your screen, press the <kbd>F8</kbd> key repeatedly (tap the key, do not keep it pressed).On certain models of laptops, you may need to keep the <kbd>Fn</kbd> key pressed down while tapping the <kbd>F8</kbd> key.</li>
 	<li>Once your system boots into the Advanced Boot Options menu, select <strong>Last Known Good Configuration (Advanced)</strong> from the list using the arrows keys</li>
 	<li>Press <kbd>Enter</kbd></li>
</ol>
<img src="/wiki/wp-content/uploads/sites/5/2013/09/Windows-7-Advanced-Boot-Options.png" />
<h3>Fix #4: System Restore</h3>
If you enabled System Restore on your computer, you may choose an earlier restore point to boot into your computer successfully.

If the 0xC000021A error is caused by an incompatible software or driver, System Restore will restore your computer to an earlier data when the incompatible software or driver wasn't installed on your system.

To do so, System Restore must be enabled on your computer prior to you installing the software or driver that caused this error.
<p class="info">If you can't boot into Safe Mode to run System Restore, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a>. EasyRE can fix this error and you can run EasyRE from any CDs, DVDs or USB drives.</p>
To run System Restore in Safe Mode, follow these steps:
<ol>
 	<li>Boot the computer</li>
 	<li>Press the <kbd>F8</kbd> key before the Windows Vista or 7 logo appears</li>
 	<li>At the <em>Advanced Boot Options</em> screen, select <strong>Safe Mode with Command Prompt</strong></li>
 	<li>Press <kbd>Enter</kbd></li>
 	<li>Login as Administrator</li>
 	<li>Type the following command, when Command Prompt appears, and then press <kbd>Enter</kbd>:
<pre>rstrui.exe</pre>
</li>
 	<li>Follow the wizard instructions to restore your computer to an earlier date</li>
</ol>
<img src="/wiki/wp-content/uploads/sites/5/2013/09/Windows-7-Advanced-Boot-Options.png" />

If you have the original installation disc with Windows Vista or Windows 7, you can run System Restore by booting into the installation disc and then going to <strong>System Recovery Options &gt; System Restore.</strong>

For more information on System Restore, go to our guide on System Restore for <a href="https://neosmart.net/wiki/windows-system-restore/#Restore_Windows_Vista">Windows Vista</a> and <a href="https://neosmart.net/wiki/windows-system-restore/#Restore_Windows_7">Windows 7</a>.
<h3>Fix #5: Last Restore Point by Command Prompt</h3>
If System Restore doesn't load, you can run the <code>dism</code> command to automatically recover the last restore point by using the Command Prompt (System Restore must be enabled):
<ol>
 	<li>Restart the computer and press the <kbd>F8</kbd> key to boot into <strong>Windows Advanced Options</strong></li>
 	<li>Select <strong>Repair your computer</strong> and press <kbd>Enter</kbd>.If the Repair your computer option isn't available, use your original installation disc to boot into System Recovery Options.</li>
 	<li>Once at System Recovery Options, select <strong>Command Prompt</strong></li>
 	<li>When Command Prompt appears, type the following command and press <kbd>Enter</kbd>:
<pre>dism /image:C:\ /cleanup-image /revertpendingactions</pre>
Replace <code>C:</code> with the letter of the driver where your Windows Vista or Windows 7 is installed.</li>
</ol>
<h3>Fix #6: Disable services in msconfig</h3>
If the 0xC000021A error is caused by a software or driver that starts when you start your Windows Vista or 7 system, you can try and disable the Services listed in the System Configuration (msconfig) utility:
<ol>
 	<li>Boot into your system
<p class="info">If you can't boot into your system because of the boot error, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a>.</p>
</li>
 	<li>Click <strong>Start</strong></li>
 	<li>Type <code>msconfig</code></li>
 	<li>Press <kbd>Enter</kbd></li>
 	<li>Go to Startup (or Services) and disable all services listed there</li>
 	<li>Click <strong>OK</strong></li>
 	<li>Click <strong>Restart</strong> to apply the changes</li>
 	<li>Restart the computer</li>
</ol>
[caption id="attachment_4592" align="alignnone" width="980"]<a href="https://neosmart.net/blog/wp-content/uploads/sites/5/2014/10/Msconfig-utility-screen.png"><img class="wp-image-4592 size-large" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2014/10/Msconfig-utility-screen-1024x592.png" alt="Msconfig utility screen" width="980" height="567" /></a> Msconfig utility screen[/caption]

If your computer works after apply the changes, the issue can be from one of the services listed in the Startup tab.

To debug which service is causing the error, boot back into the system and enable the services listed there one by one and restart the computer until you pinpoint the exact service that is causing the error.
<h2>Fix 0xC000021A on Windows 8, 8.1 and 10</h2>
<h3>Fix #1: Clean Boot</h3>
To perform a clean boot follow the steps below. A Clean Boot will allow you to troubleshoot the 0xC000021A error in-depth, if it works.
<ol>
 	<li>Boot into your system</li>
 	<li>Go to <strong>Desktop</strong> and click <strong>Start</strong></li>
 	<li>Press the [winkey] and <kbd>R</kbd> keys to open the Run utility</li>
 	<li>Type <code>msconfig</code></li>
 	<li>Press <kbd>Enter</kbd></li>
 	<li>Go to the <strong>General</strong> tab, at the <em>System Configuration</em> window</li>
 	<li>Click <strong>Selective startup</strong></li>
 	<li>Uncheck Load startup items</li>
 	<li>Go to <strong>Services</strong> tab</li>
 	<li>Check <strong>Hide all Microsoft services</strong></li>
 	<li>Click <strong>Disable all</strong> from the bottom right</li>
 	<li>Go to <strong>Startup</strong> tab</li>
 	<li>Disable all services listed there by doing: right-click on each and then click <strong>Disable</strong></li>
 	<li>Restart the computer</li>
</ol>
If your computer no longer shows the 0xC000021A error, a service listed in Startup might be the problem. To pinpoint which service exactly is causing this error, go back to msconfig and enable each service, one by one, restart the computer until the error appears again.

[caption id="attachment_4593" align="alignnone" width="980"]<a href="https://neosmart.net/blog/wp-content/uploads/sites/5/2014/10/msconfig_2.png"><img class="wp-image-4593 size-large" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2014/10/msconfig_2-1024x616.png" alt="Msconfig utility screen" width="980" height="590" /></a> Msconfig utility screen[/caption]
<h3>Fix #2: Uninstall software or drivers</h3>
A newly installed software or driver can cause this error. If Fix #1 above worked for your system, you need to uninstall that piece of software or driver.

Or, check online with the manufacturer for an updated version or a version that is compatible with the version of your Windows: 8 or 8.1

If you can't boot into your computer, try booting into Safe Mode and uninstall the necessary software or drivers:
<ol>
 	<li>Restart the computer and press the <kbd>F8</kbd> key before the Windows 8 logo appears. If the <kbd>F8</kbd> key doesn't work, try the <kbd>F11</kbd> key.</li>
 	<li>Click <strong>Troubleshoot &gt; Advanced Options &gt; Startup Settings &gt; Restart</strong></li>
 	<li>Press the <kbd>F4</kbd> key to boot into <strong>Safe Mode</strong><img src="/wiki/wp-content/uploads/sites/5/2013/09/Windows-8-Advanced-Boot-Options.png" /></li>
</ol>
If you have the original disc, you can use it to boot into Safe Mode:
<ol>
 	<li>Insert the disc and reboot the system</li>
 	<li>Press any key to boot from the media</li>
 	<li>Click <strong>Repair your computer</strong><img src="/wiki/wp-content/uploads/sites/5/2013/09/Windows-8-Advanced-Boot-Options.png" /></li>
 	<li>Click <strong>Troubleshoot</strong>, then <strong>Advanced Options</strong>, then <strong>Startup Settings</strong>, then <strong>Restart</strong></li>
 	<li>Press <kbd>F4</kbd> to boot into Safe Mode</li>
</ol>
<h3>Fix #3: Run DISM command</h3>
Boot your Windows system into Safe Mode with Command Prompt and run the <code>dism</code> command by following the steps below:
<ol>
 	<li>Reboot your system</li>
 	<li>Press the <kbd>F8</kbd> key during boot before the Windows 8 logo appears. If the F8 key doesn't work, try with <kbd>Shift</kbd> and <kbd>F8</kbd> or just the <kbd>F11</kbd> key.</li>
 	<li>Choose <strong>Troubleshoot</strong></li>
 	<li>Select <strong>Advanced Options</strong></li>
 	<li>Select <strong>Startup Settings</strong></li>
 	<li>Click <strong>Restart</strong></li>
 	<li>Press the <kbd>F6</kbd> key to boot into <strong>Safe Mode with Command Prompt</strong><img src="/wiki/wp-content/uploads/sites/5/2013/09/Windows-8-Advanced-Boot-Options.png" /></li>
 	<li>Once the Command Prompt appears, type this command and press <kbd>Enter</kbd>:
<pre>dism /image:C:\ /cleanup-image /revertpendingactions</pre>
Replace <code>C:</code> with the letter of the drive where your Windows 8/8.1/10 is installed.</li>
 	<li>Additional commands you can run are:
<pre>cd C:\Windows\WinSxS</pre>
and then:
<pre>move pending.xml pending.old</pre>
This will work if a pending.xml has been created.</li>
</ol>
If you can't boot into Safe Mode, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a>. On more information about the Safe Mode for Windows 8 and Windows 8.1 systems, go to <a href="https://neosmart.net/wiki/safe-mode/#Safe_Mode_in_Windows_8_and_81">our guide on Safe Mode: Windows 8/8.1</a>
<h3>Fix #4: System Restore</h3>
If System Restore was enabled on your Windows 8/8.1/1-, you can use it to revert back your computer to an earlier time.
<p class="info">If you can't run System Restore, go to <a href="#Fix_48120C000021A_with_Easy_Recovery_Essentials">Fix 0xC000021A with Easy Recovery Essentials</a>.</p>

<ol>
 	<li>Restart the computer</li>
 	<li>Press the <kbd>F8</kbd> key or the <kbd>F11</kbd> key</li>
 	<li>Choose a keyboard layout, if prompted</li>
 	<li>Click <strong>Troubleshoot</strong></li>
 	<li>Click <strong>Advanced Options</strong></li>
 	<li>Click <strong>System Restore</strong></li>
 	<li>Select the operating system</li>
 	<li>The System Restore will now open. Click <strong>Next</strong></li>
 	<li>Choose a restore point and click <strong>Next</strong></li>
 	<li>Click <strong>Finish</strong> to confirm the restore point</li>
 	<li>Click <strong>Yes</strong> at the warning message</li>
 	<li>Wait for the process to finish</li>
</ol>
<h3>Fix #5: Driver Signature Disabled</h3>
If you disable Driver Signature, Windows 8/8.1/10 will use drivers that aren't signed by Microsoft directly too.

This method can work if error is being caused by any of the drivers that are loading at startup.
<ol>
 	<li>Restart the computer</li>
 	<li>Press the <kbd>F8</kbd> key. If F8 key doesn't work, try the <kbd>F11</kbd> key.</li>
 	<li>Choose Troubleshoot &gt; Advanced Options &gt; Startup Settings</li>
 	<li>Click <strong>Restart</strong></li>
 	<li>Press the <kbd>F7</kbd> key to boot into Windows with the driver signature enforcement disabled</li>
</ol>
<h3>Fix #6: Reset</h3>
In Windows 8/8.1/10, you can perform a reset of your system. Before you do so, please note that:
<ul>
 	<li>A Reset will erase all personal files from your computer</li>
 	<li>If your system is Windows 8.1, a Reset will revert your computer to Windows 8. After the Reset operation is successful, you need to update to Windows 8.1</li>
</ul>
Follow these instructions:
<ol>
 	<li>Restart the computer</li>
 	<li>Press the <kbd>F8</kbd> key or the <kbd>F11</kbd> key</li>
 	<li>Choose a keyboard layout, if prompted</li>
 	<li>Click <strong>Troubleshoot</strong></li>
 	<li>Click <strong>Reset your PC</strong></li>
 	<li>Follow the instructions to complete the process</li>
</ol>
<h2>Troubleshooting the 0xC000021A error</h2>
<h3>Debug in Windows XP</h3>
While the 0xC000021A error is usually caused by an incompatible software or driver you may have recently installed, you can debug it using Dr. Watson software in Windows XP to troubleshoot its cause further more.

These are the instructions on using Dr. Watson to debug the error:
<ol>
 	<li>Open Command Prompt</li>
 	<li>Type the following command and press <kbd>Enter</kbd>:
<pre>System Root\System32\Drwtsn32.exe -I</pre>
</li>
 	<li>Type this and press <kbd>Enter</kbd>:
<pre>System Root\System32\Drwtsn32.exe</pre>
</li>
 	<li>Then select from the following options: <strong>Append to existing log file, Create crash dump, Visual Notification
</strong>
By default, the log file created by Dr. Watson is created under the following folder path:
<pre>C:\Documents and Settings\All Users.WINNT\Application Data\Microsoft\Dr Watson</pre>
</li>
</ol>
If no log file was created by the utility software, you can also use the Userdump.exe utility to create a log file:
<ol>
 	<li>Download User Mode Process Dumper 8.1 from <a href="https://web.archive.org/web/20190720211422/http://www.microsoft.com:80/en-us/download/details.aspx?id=4060">http://www.microsoft.com/en-us/download/details.aspx?id=4060</a></li>
 	<li>Run Setup.exe</li>
 	<li>Go to <strong>Control Panel</strong></li>
 	<li>Click <strong>Process Dump</strong></li>
 	<li>At the <em>Exception Monitoring</em> tab, click <strong>New</strong>. After you add the program name (Lsass.exe, Winlogon.exe, Mtx.exe, Dllhost.exe) to the <em>Monitor</em> list, click <strong>OK</strong>.</li>
 	<li>At <em>Monitor</em>, click the name you just added and click <strong>Rules</strong></li>
 	<li>Click <strong>Custom Rules</strong> and select what type of error you want to trigger (for example: Access violation errors)</li>
</ol>
Note: The User Dump utility has been removed from Microsoft's site (archived link preserved above). You can use a 3rd party utility like <a href="http://jacquelin.potier.free.fr/winapioverride32/doc/dumper.htm"><strong>Dumper</strong></a> instead to the do the same, but it needs to be run manually. Otherwise, you can follow our instructions on configuring the registry to create a crash dump.
<h2>More Information</h2>
[partial name="partial_moreinfo" versions="xp,vista,7,8,10,11,server2003,server2008,server2012,server2016,server2019,server2022"]