Your posting doesn't indicate if you've reviewed the info on that
condition at the IBM site.  If not, see that.

You could be experiencing deteriorated tapes.  A site with multiple
libraries may happen to have sets of tapes with the same serial
numbers and reintroduce a tape into the wrong library (an uncommon
cause).  Of you may have a condition addressed by a PTF.

If you do not have TapeAlert activated, consider doing so, to have a
better chance of catching problem-inciting conditions at inception.

    Richard Sims