I am running Symantic Backup Exec 12.5. I am constantly getting an error regarding one of my backups that says, Media mount failed. User canceled a Physical Volume Library operation. The data that is having problems has been backed up without any errors previously. All of a sudden, this error started happening and I can't figure out what is causing the error. There haven't been any changes to the media. The data in question is the system state of a server. Does anyone have any suggestions on how to clear this error up?