I've got an interesting problem. I migrated a user's mailbox from Exchange 5.5 to 2003, and for some reason, after the migration finished the user appeared to have a duplicated OUTBOX and SENT ITEMS folder in his Outlook 2003 client.
The user therefore deleted his duplicated folders, and these now appear in his deleted items folder.
As I believed that the duplication was caused by his .OST in 2003, I removed cached exchange mode and deleted his .OST file.
The trouble is now, when the user logs back into outlook, his working OUTBOX and SENT ITEMS folders are missing from the usual places you'd expect them (on the folder list) and now appear as subfolders in his DELETED ITEMS folder!
I'm unable to move these subfolders in outlook as I get the standard message "Unable to move special folders", and can confirm that this problem is with his mailbox as I can see the same issue when loggin him into Outlook web access.