Windows 8.1 Automatic Repair Loop – cmimcext.sys


I recently had an issue with a computer that was powered off during the installation of the November 2016 Preview of Monthly Quality Rollup update (KB3197875).

After the computer was powered back on Windows attempted to to run an automatic repair and failed. The computer would not boot into safe-mode, the only recovery option that was available was the command prompt.

Steps taken to resolve the issue

  • On the “Automatic Repair” screen I selected “Advanced option”


  • Under “Advanced options” I selected “Command Prompt”


  • I then opened the SrtTrail.txt log file that Windows creates while attempting to repair itself.  The log can be found under  C:\Windows\System32\LogFiles\Srt\SrtTrail.txt


  • The log file had the line “Boot critical file C:\cmimcext.sys is corrupt.”.

Log file cmimcext.sys

  • The cmimcext.sys file did not exist in the root of C: and the fact Windows was attempting to find the file in the root of the C: seemed very odd to me. I searched another Windows computer and found this cmimcext.sys file normally lives in C:\Windows\System32\drivers. I changed directory the drivers directory on the laptop that wouldn’t boot and sure enough the cmimcext.sys file was missing. I guess as Windows couldn’t find the file in the proper place it looked in the root of C: and rather than displaying a message that it couldn’t find the file it instead said it was corrupt.
  • I changed to the root of the C: drive on the effected computer and ran the command “dir cmimcext.sys /b/s” to search the C: drive for another copy of the file. Luckily there was one under C:\Windows\WinSxS\


  • I simply copied the cmimcext.sys file from where I had found it under C:\Windows\WinSxS\ to C:\Windows\System32\drivers
  • Rebooted Windows, at this point Windows successfully completed installing update and booted fine!

5 thoughts on “Windows 8.1 Automatic Repair Loop – cmimcext.sys”

    • Hi,

      Are you in the recovery mode version of the command prompt when you copy the file?

      Does you copy command look something like the belwo?

      copy “C:\Windows.old\WINDOWS\WinSxS\amd64_microsoft-windows-c..m-initmachineconfig_31bf3856ad364e35_10.0.15063.0_none_e7a0251a350143a6\cmimcext.sys” “C:\Windows\System32\drivers\”

      • I actually don’t have that file in windows.old? I’ve done a search and it’s in system32\drivers & c:\windows\winSxS.
        And when I try copy it, it says it’s in use.
        Yes in recovery


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