Operating system comes up with Blue Screen Error: Stop c000021a

Operating system comes up with Blue Screen Error: Stop c000021a

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In this blog we are going to discuss about how we can decode and fix operating system crashes with Stop c000021a.

Below is the first screen you will see after POST, followed by the bugcheck information.


Here is the detail bugcheck information:

The session manager initialization system process terminated unexpectedly with a status of 0xc000003a(0x00000000,0x00000000)


The second parameter “0xc000003a” resolves to “STATUS_OBJECT_PATH_NOT_FOUND”.

The first reboot after bugcheck you may not be able to get Advanced Boot Options when you press F8 and may only get Windows Error Recovery screen, as seen below.


In such scenarios there is no crash memory Dump generated.

Next thing we need to do is launch Startup Repair from Window Recovery Environment (WinRE). If you do not have WinRE installed on the machine you can boot from either Windows Server 2008/R2/Windows 7 boot disc.

Once booted into WinRE launch Command prompt and open regedit




Click on File & Load hive


Note: Whenever you are booting into WinRE you are actually booted into a RAMDRIVE. When opening registry editor you are seeing the hives from RAMDRIVE and NOT from installed Windows.  Make sure you are loading the hives from your Windows.

Consider D: as your installed drive. Browse to “D:\Windows\System32\Config” folder and select “System” hive. See image below.


Now click open and name it as “Test”.


Next step is to navigate to HKEY_LOCAL_MACHINE\Test\Select and check the value “Current”.

This dword value tells us the correct ControlSet to use.



Since we know the correct ControlSet is “1”, navigate to Controlset001 and access the following key HKEY_LOCAL_MACHINE\Test\ControlSet001\Services\mountmgr


Selecting “mountmgr”, on the right side pane look for “NoAutoMount” dword value & modify the value to “0”.

Once done, Select Test Key from top and click on File to Unload Hive. Click Yes if prompted.



Close the registry editor and reboot the server in normal mode.

More Information:

If the “Automount” is disabled it brings any Volume or Disks without drive letter offline. Additionally, entries under HKEY_LOCAL_MACHINE\System\MountedDevices key will be missing especially for Windows Boot Drive, which results in this BSOD.

Refer the link for more information on AutoMount: http://technet.microsoft.com/en-us/library/cc753703(WS.10).aspx

Jaspreet Singh
Support Engineer
Microsoft Enterprise Platforms Support

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  • Will it work on Windows 7 Ultimate x64 (without service pack)?

  • this saved my ass!

  • Tengo un Windows SBS 2001 Std ha sido reinstalado ya que presentaba errores en el sistema operativo y se reiniciaba varias veces. En el VISOR DE SUCESOS me indican que es el error 41,  que se refiere al Kernel. El sistema Operativo se encuentra instalado en un Servidor HP Proliant DL 120 G7 con 8 GB de ram, cuenta con Exchange y el sistema se encuentra totalmente actualizado. Asi mismo HP me indicó actualizar todos los drivers y también el BIOS del server. sin embargo sigue presentando las mismas fallas. HP me indica que ya no es error de Hardware, al parecer el error esta en el sistema Operativo. E

  • Is Microsoft going to create a KB article for this fix?  That would be better to reference than this 'Ask the Core Team' blog post.  Just sayin'.

  • Sorry, forgot to mention, this saved our butts too.  However this really needs to be an official KB because we could not find this on our own...we had to start a MSFT Premier Support case and have it escalated a couple of times before an engineer finally pointed us to this blog post.

  • Did a HD to SSD migration using Paragon Migrate.

    System would not boot from SSD and after trying a few things to resolve, I at least got it to the point where I was getting this BSOD.

    These instructions here worked perfectly and got the SSD past the STOP and running Windows (Win7 SP1 x64)

  • There were no "NoAutoMount" key im my registry. Adding it explicitely didn't help. Hovewer looks like the problem still was in mounting nonexisted devices.

    Fonud the solution in this thread www.pcreview.co.uk/.../stop-c000021a-fatal-system-error-session-manager-initialization-0xc000003a-t526663.html

    "Solution was to use the second win 7 to mount the system hive of the original win 7 and delete the "MountedDevices" key (Windows recreates it if its missing, and maps all drives logically)."

  • Dosent work for me

  • Thank you, This was the only thing that worked. Here is what I did in case anyone has the same trouble. all done in recovery console DVD

    1. make sure windows is c and set as active in diskpart

    2. remove drive letter for system reserved in diskpart

    3.restart, boot will fail. bootmgr error

    4. boot back into recovery dvd this time you should notice windows is actually reporting c:\windows.

    5. type bcdedit /delete {default}

    6. type bootrec /rebuildbcd

    7. reboot and enter recovery dvd again.

    8. follow Jaspreet Singh instructions above

    David Chase

    Systems Engineer

    Network Magic Unlimited

  • Well that really helped ALOT!And thx for the tip how to handle that!M$ should take a note on that article!

  • thanks

    it is a great solution when runing win 7 on virtual box in raw disk mode,on debian.

  • Originally did all of the above without the last stage - no joy.

    Setting NoAutoMount to 0 worked - thank you so much!

  • Many thanks!

    I had this problem as a consequence of deleting an Ubuntu partition and enlarging the remaining windows 7 primary partition using an old version of Parted Magic.

    I've tried all the combinations found in many forums (check disk, changing the autocheck value in the registry and so on) but this was the only working solution. Thanks a lot again.

  • Changing/setting NoAutoMount doesn't solve the BSOD issue in my case.

  • It worked in my case and thus I declare the OP to be a genius.