BE 12 kept causing end or marker on tapes

All my backups are currently failing as the jobs are causing the end of marker on every tapes in the autoloader. we have replace the drive and the autoloader as well but the problem still persist. the backup runs and then stops after a few MB's of data written and then the tape will be ejected from the drive back to the slots with end of marker stated. we have replace the drive and autoloader, new tapes and create new jobs, but the job still failing out of sudden, any ideas on this as I am totally out of ideas now.