John -

The joy of inherited environments, where you have no solid
information on how things were configured by your predecessors...

In my experience, an ANR8469E unload failure is always due to a tape
drive hardware problem (possibly a sensor or motor problem).  Check
your records or logs to gauge whether one or two drives are
troublemakers and need work.  A tape stuck in a drive tends to stay
in the drive, where it subsequently being put away in a strange place
*might* be due to human actions.  Sometimes, a seeming unload failure
can be a timing problem in the drive microcode, where not enough time
is being allowed for the operation.

See IBM Technotes (1143428, 1212674) on the possible causes of
ANR8356E.  An insidious problem is where the barcode is inconsistent
with the magnetic labeling of the volume.  Element number
inconsistencies are another gem.

Beyond that, I would activate TapeAlert and review AIX Error Log
entries.  You also say that you are doing library sharing, so I would
review the logs of both sharers and see if both are experiencing the
same kind of problems, which may illuminate configuration or software
issues.

  what I can think of,  Richard Sims