How to Fix Stop C000021a Error in Windows
All versions of the Windows operating system use winlogon.exe and csrss.exe but if you've recently install new drivers, system services, or programs in Windows, you likely encountered the stop C000021a error message because of the said changes on the system.
To try fixing C000021a error in Windows, you need to determine if there is third-party GinaDLL:
- Open registry editor in Windows by typing regedit.exe in the run box. Hit enter key on the keyboard.
- Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
- In the right pane, determine if there is GinaDLL REG_SZ value.
If GinaDLL is present, the cause of stop error c000021a is most likely from the changes made by the software or hardware vendor to the system which you installed.
Fix it by using updated software or remove the recently installed software or driver. Report the issue to the software and hardware vendor so they will fix their program. If you cannot remove the software or driver due to BSOD when starting the computer, you can try using the recovery console or system restore function in Windows. Don't forget to first try using Last Known Good Configuration option to boot the computer before using restore or recovery features.
Note that Windows 7 users may use the Startup Repair function included in Windows 7 installation DVD.
Advanced users can also fix the problem by replacing GinaDLL. You can use Bart's Preinstalled Environment (BartPE) bootable live Windows CD/DVD to copy Gdi32.dll and replace the existing dll file in system32 folder of Windows. Another option is to install Windows in another partition so you can access the system that is experiencing the stop C000021a problem.