Danny,
Have you fixed this problem? I have also exact situation. We bought Tandberg LTO2 420, but couldn't get it to work with BE 9.1. I haven't tried the OEM though. But when I used it with BE 9.1 driver, I got the exact same error "invalid physical library argument" and the tape will be ejected. It worked okay with NTbackup. Please tell us if you resolved the problem. I just can't justify spending $1200 for BE 10.0 because Veritas doesn't have a driver for LTO2 420.
Thanks