You may be able to run diagnostics to try to get information on what's going on. Definitely inspect OS logs and the TSM Activity Log for any details on the error condition. Also, verify that your drive and library firmware levels are at an appropriate version: replacement drives may come with an old firmware level, which could cause problems. Your tape drive technology may support TapeAlert, which could then be turned on. If still problematic, you could try putting suspect drives offline to try to isolate the troublemakers. An unlikely cause of problems would be a bad batch of tapes. (I once unspooled a name-brand problem tape to see if it had a physical media problem - and actually found a factory splice!)
Richard Sims