Seen a few Windows 10 PCs display an alert dialogue when attempting to run any MMC snap-in (e.g. Services, Local Group Policy etc). The dialogue helpfully states that an “administrator” has blocked you from running this app, and the only option is to close the box…
The quick and dirty workaround is to run an elevated command prompt and run mmc from there and manually load whichever snap-ins it is you need.
The “fix” (not that you can really call it that), is as follows:
Find another PC with working MMC… Navigate to C:\Windows\System32\CatRoot
Copy all .cat files to the plagued workstation in the same folder.
Do *NOT* overwrite files.
If it still does not work, repeat steps 1 and 2 and DO overwrite the files.
More detail can be found in an MS community article by HDJam.