After upgrading from SP3 to SP4 on several Windows 2000 PRO machines everything looked fine, but from time to time applications can't write to the event log.
When I try to view the application event log it appears to be empty. If I "clear all events" and re-start the service, the problem is fixed and applications can write to the event log. But it usually repeats itself after a few hours/days.
I could replicate this problem several times and it is very disturbing because I have many applications writing to the event log.
The application event log is set to "overwrite events as needed'.