I back up my Pro Tools audio and session files (Mac-based) with Retrospect (vs. 4.3) to a Sony DDS-3 Tape drive. For years I hardly had any execution errors, but now I get 25-30% of my files coming back with errors. Repeating the back-up a few times sometimes works, but sometimes after many repeated back-ups of the same data, there are still two or three files that don't get copied properly.