The association somehow got screwed up for
.msc extension. Go to the
windows\system32 folder and look for
mmc.exe (Microsoft Management Console).
If it is there, go to tools, folder options, file types and look for the msc extension, highlight it and go to the change button, browse to the system32 folder and click on mmc.exe.
Or click on the
defrag.msc and open with, browse to the
system32 folder and
mmc.exe and don't forget to check the box for open all files like this with this program.
If you don't find mmc.exe in the
system32 folder, copy one off of another computer and paste it into the
system32 folder on the problem machine, then associate the
msc files with it. 😎