Fix 0xc000021a Error in Windows 10 & 8

I just updated my Windows and now I am getting a BSOD with error code: 0xc000021A after restarting my PC

Windows errors are not a new thing, but the error codes always seem to surprise me. And, despite some BSODs being as dangerous as they are, you can never measure the fatality of a problem.

One of those BSOD errors is 0xc000021A. The error 0xc000021A can be caused due to a simple file or a whole hardware failing.

But how dangerous is it? what caused it? and more importantly how to fix it? In this article, I will tell you about the error and how to fix 0xc000021A error.

What is 0xc000021A and How to Fix it?

The 0xc000021A is an error which is seen after an update or while installing a new Windows. You get this error when Windows feels like its security is compromised. In such cases,  Windows shows a BSOD to stop further damage and requesting external help.

The error 0xc000021A is caused when any of the two major components of Windows User Mode SubSystem either misbehave or gets corrupted. Those two SubSystems are-

  • The Winlogon.exe
  • The Client-Server Run-Time Subsystem (CSRSS)

As any of these two files starts malfunctioning, Windows shows you error with error code- 0xc000021A. Some of the possible errors are-

  • STOP 0xC000021A
  • STOP c000021a
  • HALT: c000021a

So long story short, this error is caused when system driver, software or registry starts malfunctioning. And, no matter how complicated it sounds, it is a BSOD which means we can solve it using traditional methods. But before that let us get you out of the restart loop first.

1. Break Boot Loop

Note: Skip this process if you can access your Windows

The biggest reasons with BSODs is that most of the time we get a stuck in a loop of restarts. And to break this loop, you will have to boot your PC in safe mode. In order to do so, you will need a bootable device with Windows 10 on it. Once you get that, follow-through-

  • Insert a bootable device, and boot/reboot your PC. Navigate through bios to access Boot menu. You can also do it directly by holding a pre-assigned key. For my PC it is the Del key.
  • Now select the inserted Bootable device and go to the Windows Installation screen
  • On the installation screen, click on  Repair your computer on the left bottom corner of the screen.

  • Now navigate through Choose an Option-> Troubleshoot-> Advanced Settings -> Startup Settings.

  • Under the Startup settings, press F4 to boot in safe mode.

2. Perform SFC and DISM

After your PC has booted, it is time to run some scans.  These scans will not only help find the problem but will also fix them immediately. And since it is a Windows files and drivers issue, nothing works better than SFC and DISM scans.

System File Checker

The SFC or System File Checker is a built-in Windows tool. This tool first scans your Windows files to find any type of corrupted or damaged file. Once the file is spotted, it then replaces it with the original copy of the same file. To run SFC scan,

  •  First, open Command Prompt as admin like above.

Use cmd as admin to run sfc/scannow

  • Once it is opened, type in “sfc /scannow” and press Enter.
  • Now, wait till the scan is complete and move to the next one.


The DISM or Deployment Image Servicing and Mangement tool is used to fix or repair Windows image files. It is a command-line tool that helps repair (.wim ), (.vhd), (.vhdx), (.ffu) etc. To run DISM,

  • First, open Command Prompt as admin.
  • Then type the following-
  • Dism /Online /Cleanup-Image /CheckHealth” then press Enter.
  • Dism /Online /Cleanup-Image /Scan-Health” then press Enter.
  • Dism /Online /Cleanup-Image /RestoreHealth” and press Enter again.

  • Reboot your system to check if the problem persists.

3. Disable Driver Signature enforcement(Win 8/10)

The Driver Signature enforcement is a Microsoft tool that allows Windows to load only Windows driver. It basically allows Windows to separate external drivers to Microsft signed drivers. So every time to lof in Windows only consider Microsoft’s drivers while other drivers are not accounted for.

This can force Windows to think that other drivers are compromised, and hence it shows an error. But, it can be solved by disabling them. To do so, you will need to access Startup Setting. You can do that by following Method 1.

  • On the  Startup Setting, press F7 to disable Driver Signature Enforcement.

4. Run System Restore

If none of the above methods worked out for you, then restoring Windows might be your only option. By doing so your Windows will go to a previous stage without losing any data. An alternative to this step could be re-installing your Windows, which will beat the whole point.

To restore your Windows,

  • First, press Windows+ R to open Run. Now type in rstrui.exe and press Enter.

  • Now in System Restore, click on Next to proceed.
  • Here choose the latest restore point and click on Next.

Choose a restore point to restore your PC

  • Finally, click on Finish to perform system restore. This should definitely solve the issue.

Final Words

The error 0xc000021A is not a common error, nor it is a fatal one. But the fact that you can’t boot your PC makes it really annoying.  The cause of this error is a little complicated, but solving it won’t take long. But just to be one the safe side, make sure that you have your data backed up. As if none of the methods work, you will only be left with two options either reset or reinstall your Windows.

You can also perform SFC and Dism scans regularly. These will help you predict any upcoming error and prevent it. Also, keep your system up to date, and regularly perform a full system scan to prevent errors.

With that said, I think I shared everything I could on this topic. I hope these methods help you solve your issues. If you have any queries, feel free to ask in the comments.

Leave a Reply

Your email address will not be published.

You May Also Like