When trying to perform certain database functions sometimes you need to be the sole user. If not you may see an "unable to open database exclusively" or "other users currently connected" message when trying to update or work on the database files. If you have the client-server editon of Probate Plus you can simply examine the "Configure Database Connection" screen. The active users will be displayed at the bottom of the database configuration dialog box.
If you have the peer-to-peer edition of Probate Plus you'll need to examine the in-use sessions for the database folder in question. You can find the in-use sessions by using computer management in Windows and checking the session list.