DDS tapes report as erased

I have a problem with tapes that we have archived jobs to. When trying to
pick up jobs, some of the tapes report back as erased. These tapes are
not erased. Sometimes if we pop the tape out and retry a number of
times it will locate the files. Some we can’t retreive from at all.

These are tapes we backed up to in 2007.

Does anyone have an idea what is causing this?