After a server crash at work I came across this error when trying to access active directory users and computer
MMC cannot open the file C:\WINDOWSWindows
\system32\dsa.msc.
This may be because the file does not exist, is not an MMC console, or was
created by a later version of MMC. This may also be because you do not have
sufficient access rights to the file.
I tried a number of solutions but the only one that worked for me was to recreate the mmc file
If you have the same problem just try recreating the file
# Start
# Run
# MMC
# File, Add/Remove Snap-in
# Click Add
# Select Active Directory Users and Computers
# Click Add
# Click Close
# Click OK
# Click File then SAVE as
# Point the browser to C:\Windows\System32\
# Name the file dsa.msc and replace the existing file.
Try loading active directory users and computer and all should be OK 
If there any other *.msc files that are doing the same thing, follow the same process but change accordingly
