My guess its a 3rd party program screwing stuff up. Disable antivirus and
another such programs.
Also look in Event Viewer for ESENT errors. If your message store database
is screwed up with permissions you'll get an error 5 (access denied), which
means you'll have to take ownership of the message store directory and then
reset the permissions. But you should get some sort of error message with
nonsense like you don't have enough disk space or memory, so I'd guess door
#1, its a 3rd party program.
steve