KB5077181 was released about a month ago as part of the February Patch Tuesday rollout. When the update first arrived, users reported a wide range of problems, including boot loops, login errors, and installation issues.
Microsoft has now acknowledged another problem linked to the same update. Some affected users see the message “C:\ is not accessible – Access denied” when trying to open the system drive.
Security to some level is important, but whatever idiot at msft sold exec on “user access control” as a standard service really effed windows hard. Security types have a role in the world, but a lot of them are authoritarian idiots. One of those idiots wrote this patch, and msft was so used to UAC problems in everything, they just let it on through during testing.