On Exchange 2003, Calendar items are becoming corrupt in OWA (displays HTTP/1.1 500 Internal Server Error) only when receiving the acceptance of the invitation from gmail.com or live.com mailboxes. This is sporadic (same steps will not produce the corruption all the time) but probably half of the time. The calendar items can be viewed correctly always in Outlook but not in OWA.

Sounds like it's time to upgrade to Exchange 2010. These kinds of things won't be fixed in Exchange 2003 any more.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."