OK, I did some testing.
That error appears if you select the CURRENT boot drive in the pop-up menu. You're supposed to select the drive you want to become the new one. So it looks like you're selecting what already is the boot drive....
I've fixed the bug anyway, and have attached a build that doesn't show that error.
However, you must select the destination soon-to-boot-drive in the pop-up dialog..
That error appears if you select the CURRENT boot drive in the pop-up menu. You're supposed to select the drive you want to become the new one. So it looks like you're selecting what already is the boot drive....
I've fixed the bug anyway, and have attached a build that doesn't show that error.
However, you must select the destination soon-to-boot-drive in the pop-up dialog..