Did you ever do this: save a message or attachment to your hard drive then decide to move the folder the items were saved into only to have Outlook tell you the folder is in use by another user?
You (and Outlook) are the other user. Outlook keeps a lock on the last folder used and when you save something from Outlook again, Outlook defaults to that folder.
The workaround is to pretend to save another item and select a different folder, then cancel the save. Outlook will use this folder as the new default and you can move or delete the other folder.
Closing Outlook will also release the lock, but it’s generally easier to do another Save as and select a different folder.
