There?s no one clear cut answer to this problem, but here are some areas to explore:
Does the user have access to another?s mailbox with an erroneous name?
Under Outlook 2000-Tools-Services-Microsoft Exchange Server-Properties-Advanced-"Open these additional Mailboxes"
Are there multiple archive.pst files?
Can you open the archive PST via File>Open>Personal Folders? Is the file near the 2GB limit.)
Check the default AutoArchive properties and the autoarchive properties for each folder. Make sure that the references are to existing PST files (with a correct paths)
Check what services are installed. Tools>Services?
Are they all still valid?
Try the Inbox Repair Tool and run Scandisk.
Does the user have read/write permission for the archive file location?
If you can locate the archive log, it may provide a more detailed error record.
Good luck!