Internal MAPI Error.

I have Outlook loaded on remote Exchange Servers for Backup Exec to use to send notification messages. After a week or two the messages will stop being sent. I thought this had to do with memory leaks in SP3. I have since upgraded to SP5 and the problems continues. When I try to start Outlook on the server I get the error “Internal MAPI error has caused this logon attempt to fail – MAPI 1.0 (000004C2)” Rebooting solves the problem for another two weeks. This occurrs on multiple servers.