Getting error c000021a: The session manager failed to create protected prefixes

When I try to boot Windows I get a blue screen:

STOP: c000021a Fatal System Error .

The session manager failed to create protected prefixes system process terminated unexpectedly with a status of 0xc000003a (0x00000000 0x00000000).
The system has been shut down.

And the system reboots.

Just yesterday Windows installed some patches through "Windows Update". So I tried different Windows start options and only one worked and the system booted which was

Disable Driver Signature Verification

Now my system is running but I wonder what to do so I can start Windows normally in the furture. Until now I did not dare to reboot again.

What I tried so far:

• SMART check of HDD with Speccy is OK
• CHKDSK reports 98336 KB in faulty sectors
• SFC reports that it could not repair some damaged files

Stop C000021a is fatal system error that occurs early in the boot process during initialization with the Session Manager. The status code 0xc000003a indicates STATUS_OBJECT_PATH_NOT_FOUND. You may work around the issue by disabling integrity checks or by permitting test signing on drivers on boot.

The issue is evidently being caused by a device driver that is corrupt or not properly signed. Disabling Driver Signature is of course not an acceptable workaround.

I will describe below a procedure for testing where is the error and of fixing it. If when following it you encounter any error condition, report it in your post and do not continue.

Step 1 : Corruption checks

To check for corruption execute the following :

• S.M.A.R.T. test to check for general disk failure using a utility such as Speccy. For interpreting the results where unclear refer to this answer.

• Run the command chkdsk C:. For more information see this article, but in case of error, report to us and do not execute yet any of the repair options.

• Run sfc /scannow to check Windows integrity as described in this article.

If all tests have passed, continue on.

Step 2 : Locate bad driver

List the drivers as they are being loaded during the boot process in an effort to determine which driver may be causing the crash, returning driver checks, by running in an elevated Command Prompt (cmd) the commands:

bcdedit –set sos on
bcdedit /deletevalue nointegritychecks  
bcdedit /deletevalue testsigning

Reboot and tell us the name of the last driver to be displayed. If the name disappears too fast when the crash occurs, film the boot process using your telephone.

Let us know which driver it is before continuing.

Once the bad driver is identified, you may :

• Disable again Driver Signature Verification and boot
• Enter Device Manager and locate the faulty device
• Right-click it and choose Uninstall device
• Depending on the driver, you may be given the choice of deleting it, but wait for our OK
• Return Driver Signature Verification and reboot
• If this works but the related device doesn't work any more, you may need to download a driver from the manufacturer's website.

If the above has not helped, continue on.

Step 3 : Take backups

Disable again Driver Signature Verification and boot to save all your files.

I also suggest that you take as backup an image of the system disk on some external disk. My favorite product is AOMEI Backupper freeware. If you use AOMEI, create an AOMEI Bootable Disc or USB as described here, boot it and verify that it can see your backup, just in case.

Step 4 : Repair Windows

Disable again Driver Signature Verification and boot into Windows. Do a Repair Install from your boot media as described here. It is important to use a boot media that corresponds to your service-pack level (SP1?). This will conserve your applications and drivers and most system settings.

If Windows can then boot with Driver Signature Verification enabled, then all is fine. Execute Windows Update repeatedly until all updates are done.

Otherwise, you are in trouble and need to reinstall Windows from scratch.