The tape may still be bad.  How long ago was it that the tape was written
on.  Has it been exposed to heat etc.  These could all be factors to the
tape being bad.  I have seen tapes go bad for all sorts of strange reasons
some seen and some unseen.  If you try another tape do you get the same
error?  If so you can bet you have a bad tape drive.  If you don't then
mark the tape bad and move on.

Forrest