One thing I'd try in debugging your problem is to use the mtlib command
to issue requests external to *SM, starting with a timed loop of query
commands, logged with times so as to see when you get communication
failures.  Thereafter have it do mounts when there will be no conflict
with *SM.

Also do the obvious and check that your serial cable is intact and that
its connections are solid.  That connection goes through the ARTIC panel
in the 3494 and the ARTIC adapter card in the industrial PC.  We've had
two failures of the ARTIC adapter card in the past six months.  Another
ADSMer reports the same problem as you're having, but using TCP/IP
instead for communication, so I doubt ARTIC problems.  My gut feeling
would be compatibility problems between the new Library Manager level
and the atldd software, which is always a joy as there is little or
no compatibility guidance that I've seen.
      Richard Sims, BU