Windows3k Enterprise server

Cannot access Application event log getting message
"unable to read the contents of this event log" and refreshing App Evt
log will also give same error message.

When this happens, I also get "Cannot open application: Error while
opening key" message
when trying to access
"HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Eventlog\Application"
key

What could be the cause of this situation? How to determine which
process has a lock on Application Event log? Thank you.