For what it is worth, there is a hardware/software standard for diagnosing problems with tape hardware. The standard is called "TapeAlert", and a website, TapeAlert Specification has info on it.

According to the site, basically all of the hardware supports it, and there are software products available for all operating systems that can interface with it. This gives you much better information than you can get from the O/S, or whatever backup software you are running.