What type of drive was this session copied from? Did you check permissions on the drive an any enclosing folders for the session, as well as any audio files used in the session? You may try doing a 'save session copy in' from the File menu and choose to copy all audio files, then close the current session and open the one you just saved. Are you able to work without the error? Sometimes not haveing the most current Pace drivers can cause this problem, though it's usually related to using plug-ins. You can get Pace drivers from their website .