In one case, a faulty drive (18 gig Seagate Cheetah) was to blame:User confirmed this by attempting a LOW LEVEL format...the process never completed and the system hung. NOTE:-Early in troubleshooting this problem the drive was formatted (quick erase: high level format) and that worked fine. But once data was copied back on the drive the DAE -4 error immediately came back up. Performing a low level format was the only thing that clued us in to the fact that the drive mechanism could be the culprit.Another clue as to the problem were media errors posted by Retrospect when performing a backup. This drive was approx 4 months old.