Voices for Tracks are tied to the Disk I/O and Drive. In expanded PT (32- or 48track) systems, you cannot play an audio file from a B (or C) drive that's on a track set to an A voice. If you move files between drives, or swap drives between Disk I/O's, this error will be posted when opening the session.If this message appears when using a single Disk I/O system, it is likely that a copy of the session folder has been made onto another drive.Throw away the copy or unmount the drive before opening the session.