I have been fighting this problem for weeks and cannot resolve it unless I Uninstall and reinstall Exchange and reload the mailboxes from PST's Which has not been truely successful. The error in the agent log and event log both say 'FATAL Error (0x86664004)occured in an Iexchange eventsink while processing (Subject=Message) CDO Error 80004005 Description [Collaboration Data Objects-[E_FAIL(80004005)]]' This is drving me insane..The vbscript is from the Tom Howe Office Calendar for Exchange 5.5 from Slipstick It worked for several weeks then quit...I am really struggling here so if you have anything that might be useful please advise. I have tried uninstalling the Event Service and uninstall/Reinstall Outlook XP but to no avail......