I got a "security log is full" message when trying to log into a windows XP machine.
I know, why are we still using XP? We have to for a hand full of applications that still require it.
Anyway, the user that was trying to login was an Administrator on the PC, but it still would not let them log in.
I ended up logging in as a different Administrator and it let me in fine.
Then I went to Computer Management and under the Administrators group sure enough the one that was trying to login is already in there.
Any ideas why that user could not log in because the Log was full even though they were a local Administrator?
1. Click Start, point to All Programs, point to Administrative Tools, and then click Event Viewer.
2. Right-click Security, and then click Properties.
3. In the Log Size area of the Security Properties window, click the Overwrite events as needed option under When maximum log size is reached.
4. Click OK.
5. Close Event Viewer.
That should take care of it for you.
https://support.microsoft.com/en-us/kb/867860