How to Fix the 0xc000021a update error on Windows 10?

A Blue Screen of Death (BSOD) is used to display a stop code in the event your system unexpectedly crashes. The BSOD is sometimes a one-time error, but usually signals a serious problem that needs addressing. The blue-screen allows you to identify the specific stop code, so you can troubleshoot the problem. In this article, we will cover the Windows update error that comes with the stop code 0xc000021a, and what you can do to fix.

0xc000021a BSoD error screen

The other associated error codes you may see with the 0xc000021a error include:

  • c000021a {Fatal System Error}

What causes the 0xc000021a update error?

Microsoft has continued to improve and iterate on it’s Windows 10 operating system to limit problems that users encounter. However errors can crop up during updates and system changes too. The error 0xc000021a is usually triggered by updating the operating system to from Windows 7 or 8.1 to Windows 10. This error is particularly nasty, because it can cause a continual BSOD boot loop.

The error can also happen when a user-mode subsystem in Windows becomes corrupted. There are two Windows user-mode subsystems that are usually associated with this error:

  • WinLogon
  • Client Server-Run Time Subsystem (CSRSS)

It’s not vital here to understand what these subsystems do, just how to fix the problem. The solutions on this guide are for Windows 10, so please check your version of Windows before continuing.

9 proven solutions to the 0xc000021a Windows update error

Below are the nine best options to solve this BSOD error. There is a big difference in how you can troubleshoot the problem depending on if you can log in to Windows and perform actions, or if you are stuck in a constant boot loop.

Method #1 and #2 are your best bets in both cases. Then, methods 3-8 cover additional solutions for those who can access the Windows user interface. Finally, if nothing helped so far, method #8 and #9 are last resort fixes.

1. Unplug External Devices

Peripherals can interfere with how the computer interfaces with user-mode subsystems, causing critical errors. This can trigger the 0xc000021a error. If you are encountering this blue screen error, unplug all external devices. Leave only the mouse and keyboard for navigation during boot. Unplug any storage devices like flash drivers or external hard drives. Restart the computer and see if the problem reoccurs.

2. Startup Repair

This solution will fix the 0xc000021a error in most cases. This method is also great if you’re stuck in a Windows 10 boot loop and can’t access the Repair options from the desktop.

Here is how to perform a Startup Repair:

  1. Start your computer by pressing the Power button.
  2. When the Windows 10 splash screen appears, immediately turn off the system.
  3. Do this 2 more times and Windows will recognize there is a problem and load the Recovery Environment where you can access the repair options.
  4. When the screen says Automatic Repair, click Advanced options (or Troubleshoot, then Advance options).
  5. Select Startup Repair.
Startup Repair

This will repair the startup process and should fix any startup errors. When this process is finished, reboot your system normally.

3. Perform a Clean Boot

The second fix is to clean boot your system. Performing a clean boot can help isolate the Windows service that may be causing the error.

To clean boot your Windows system:

  1. Click the Windows Key (between Alt and Ctrl on your keyboard) + R.
  2. In the Run utility window, type “msconfig” and press Enter.
Run msconfig
  1. In the System Configuration Window, make sure you are in the General tab. Then Click Selective Startup.
  2. Uncheck Load startup items.
System configuration settings
  1. Navigate to the Services tab and check Hide all Microsoft Services in the bottom right, and then click Disable all.
Disable all services
  1. Finally, in the Startup tab, disable all services individually by right-clicking and then selecting Disable.
  2. Now restart your system.

If the BSOD error does not return, a Windows service that loads during Startup, may be to blame for the error. The specific service can be identified by repeating the process and enabling each service one at a time. Restart the computer each time. Only select one service each time. If the 0xc000021a error reoccurs, the last service you enabled is likely the root problem.

4. Run the SFC scan tool

Microsoft has included a tool called the Windows System File Checker (SFC), in Windows 10 (as well as other modern Windows versions. This tool can repair corrupted system files that can prevent the system from booting properly and trigger a BSOD.

  1. Click the Start Menu button and search for Command Prompt.
Open the Command Prompt
  1. Right-click the app, and select Run as administrator.
  2. In the Command Prompt window, type in: sfc/scannow
  3. Then hit Enter.
SFC /scannow command
  1. Wait until verification is at 100% complete.

If the tool finds no integrity violations, that means that no system files were missing or corrupted. If the tool cannot perform the requested operation, the scan will need to be performed in Safe Mode. The tool may find corrupt files and try to repair them, after that you can restart your system and check for the error.

Note: If you run into an SFC /Scannow error when starting the scan, don’t worry. We have written dedicated articles on what to do if SFC scannow is not working, including:

5. Disable Driver Signature Enforcement

Driver Signature Enforcement is enabled to act as a security measure against malware by making sure all drivers have been signed by Microsoft. Only those that are signed can be loaded into Windows kernel. If this feature is interfering with the system, it can be throwing this BSOD error unnecessarily. You will need a bootable Windows DVD or flash drive to use this method. To disable the driver signature enforcement:

  1. Boot your system using a Windows 10 bootable DVD or flashdrive.
  2. Select Troubleshoot and then Advanced Options.
Windows RE troubleshooting advanced options
  1. Select Startup Settings and then select the option to Disable Driver Signature Enforcement by pressing F7.
Disable driver signature enforcement
  1. Restart the system without the bootable media and see if the error reoccurs.

6. Run the DISM Command

A similar tool to SFC, is known as the DISM command. DISM stands for Deployment Image Servicing and Management Tool. This tool can repair your Windows installation media.

  1. Open the Start Menu and search for Command Prompt.
  2. Right-click it, and select Run as administrator.
  3. When the Command Prompt opens, type in:
    DISM /Online /Cleanup-Image /RestoreHealth
DISM /Online /Cleanup-Image /RestoreHealth
  1. Wait until the process is complete and don’t work on anything else while you wait.

7. Update your drivers

Checking and updating any drivers is a common troubleshooting step. Drivers essentially allow software to communicate with hardware. During this ‘translation’ process, any errors can become magnified and lead to an array of errors including full system crashes. To check your drivers:

  1. Right-click the Start Menu and select Device Manager.
Open Device Manager
  1. Expand each section in the Device Manager to see hardware with associated drivers.
  2. Right-click each device and select Update driver.
Update drivers
  1. Windows will automatically search your system and the internet for the most up to date drivers. If an update is found, it will be applied.

Once this process is complete, restart your system and see if the problem has been fixed.

8. Perform a Windows reset

If the previous solutions didn’t help, or your system is stuck in a boot loop and you can’t get past the BSOD, here is a last resort option. Make sure to try the Startup Repair method first that we explained in the first solution. If that didn’t fix the problem, then your only choice might be to reset your Windows system.

Warning: This is a drastic solution because the reset will wipe your OS drive and erase all of your personal files.

It’s very important to regularly back up your hard drive to prevent loss of important files in the case of a catastrophic error.

If you fully understand the consequences, here is how to perform a Windows reset:

  1. Start your computer by pressing the Power button.
  2. When the Windows 10 splash screen appears, immediately turn off the system.
  3. Do this 2 more times and Windows will recognize there is a problem and load the Recovery Environment where you can access the repair options.
  4. When the screen says Automatic Repair, click Advanced options.
  5. On the Choose an option screen, select Troubleshoot.
Windows RE troubleshooting
  1. Select Reset this PC.
  2. Select Fully clean the drive.

The reset will revert your system back to its original Windows version. You may then need to update to Windows 10. This process will take a few hours. Do not unplug the computer during this time.

9. Reinstall Windows from bootable USB

You can also opt to perform a fresh installation of Windows 10 using a bootable USB. The USB should have at least 8GB of storage capacity and should be checked for any important files beforehand. Another computer will need to be used to create the bootable USB.

Here is how to reinstall a clean Windows 10 OS using a bootable USB drive:

  1. Connect your USB stick to a working computer.
  2. Right-click the Windows Start button and select Disk Management.
  3. Find the USB partition and right-click Format. The FAT32 file system should be selected to boot based on a BIOS or UEFI system.
  4. Right-click the USB partition and select Mark Partition as Active.
  5. Use Windows 10 Create Installation Media tool to load Windows 10 installation media onto the USB flash drive.
  6. Now connect the USB to the faulty computer where you want to reinstall Windows, and turn the machine on.
  7. Load into the boot-selection menu by pressing Esc/F10/F12, depending on the machine.
  8. Select to boot from the USB and follow all directions to install Windows 10.
  9. When the installation is complete, remove the flash drive.

This should solve any critical system errors that can potentially trigger the 0xc000021a error.

Problem Fixed

Hopefully one of the above solutions helped solve the 0xc000021a Windows update error plaguing your system. These steps are aimed to guide you, step by step, through the common troubleshooting solutions. Even though BSOD errors are a pain, troubleshooting will teach you valuable skills in navigating your Window’s operating system. Windows has a variety of tools and safeguards in place to protect your data and help you fix problems and recover your system.

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