Interestingly, Apple Mail will have no difficulty syncing and, have the correct message count for the Inbox folder when Outlook 2011 is having the problem.I suspect Entourage Web Service edition may work too.I cannot see any correlation between name or number of contents when looking at the files that are not on the Exchange server.The total size on the Exchange server is about 1GB, which is well under the store limit for this box.I started looking, and her outlook 2011 did not reflect all calendar entries (not even 10% of them).
Entered his Exchange account and let it download all messages, again this had rebuilt the entire profile, but still the issue remains.
They are viewing other empoyee's calendars, not the entire mailbox.
So there are no additional 'mailboxes' being opened, Just shared other user's calendars.
Using Outlook Web Access I sorted by type, found the meeting invitation which appeared in the OWA Inbox but not in my Outlook 2011, I deleted it from the Inbox and Deleted Items folder.
After doing this my Outlook 2011 began updating quickly and correctly.