I ran into a similar problem a few years ago when I upgraded my tape drive from a QIC to a DAT Autoloader(Compaq). The drive didn't like the brand of DDS tapes I was using and I got an error message from ARCserve(5.01).
I found a switch setting in the drive documentation that set Media Recognition ON/OFF and set it to off, that fixed the problem. The drive documentation recomended a different brand of tape and the Media Recognition was very particular?
Anyway, the drives and tapes work great and I'm now on my second set of drives and expanded library of tapes running on ARCserve 6.6.
HTH
Ken