is this the only hour that is failing to unscheduled? Have you tried un-scheduling any other hours or days in the log?
Sometimes if the hour is open somewhere, (someone has left the Segue Editor open, or the log is in preview mode) then the hour is open and locked and cannot be unscheduled and removed.
Go around to all your Myriad terminals and check that the hour has not been loaded anywhere.
If that doesn't help, close the database on ALL terminals and try to compress / repair the database.
When you say that you have moved computers, do you mean that you have moved where the databases are stored? If so check the user permissions to make sure the logged on Windows user (on the PC where AutoTrack is running) has full read / write access to the server location where the databases are.
Broadcast Radio Ltd