There is a bug with Windows AIO repair. After I run the repair "register system files", if I have the Remote Server Administration Toolkit (RSAT) is installed on my machine and I try to open "Active Directory Users and Computers", I get the above error and the one attached to this post. I already found the fix: I simply have to re-register all of the dlls in the "System32" folder with the below command, and it starts working again immediately:
for /f %s in ('dir /b *.dll') do regsvr32 /s %s, C:\Windows\system32
EDIT: Usually this resolves the issue. However, and I don't know if Windows AIO repair causes this issue or not, but the above command did not fix it for me this time. It took me a lot of research to find this, but the reason that the error is occurring is because certain registry keys were improperly modified:
HKEY_CLASSES_ROOT\mscfile\shell
When I expanded Author\command, open\command, and RunAs\Command, the default registry key for each entry was pointing to the 32-bit version of the mmc executable in '%SystemRoot%\SysWow64\mmc.exe "%1" %*'. These registry keys need to be changed to point to the mmc executable in the "system32" folder instead. Then it worked like a charm.
