HELP!
"Unable to display the folder. Microsoft Office Outlook could not access the specified folder location. The messaging interface has returned an unknown error. If the problem persists, restart Outlook. Access is denied. Make sure the disk is not full or write-protected and that the file is not being used.

I get this regardless if the user is on a Windows XP with Office 2003 or Windows 2000 with Office 2003. There mailbox opens fine and all my users have a personal folder (PST file) to store there old emails, etc. The location of the PST files have not changed (located on there home directory). For some users, they never have a problem, others report after being in outlook, say an hour or longer, and when they click on there personal folder they get the error listed above. If they close outlook and reopen it, it works fine again. I have checked our network connections and everything is fine, no dropped connections. I have searched KB articles till I'm blue in the face. I have found nothing that works. The only thing that has changed is all of our servers have now been upgraded to Windows 2003 Int servers. We are an entire Windows shop with all updates are applied within 24 hours of release

Any help on this issue would be greatly appreciated