Problem with meeting requests

Installed Exchange 2003 SP1 on a SBS2003 last night. This
morning when users receive a meeting request in their
inbox and try to click on it, they get a "Can't open this
item" error message pop up. The message can't be moved to
another folder and if you try to delete it it complains
that only the header has been downloaded. You can mark it
for download but it never seems to. This is occuring on
Outlook 2003 running in cached exhange mode. I have
switched off cached mode, but the problem stays the same.
Interestingly, using OWA everything is fine. The request
can be accepted, deleted, whatever. This only seems to be
a problem with outlook.

Any Ideas?

Thanks,
Joe Boren