I can't believe that there's no other person who had ever had similar
errors.
So again:

Hi ADSMers all over the world!

We have some problems with our storage-equipment:
adsm-server V3.1 on AIX 4.1.5, STK9710 library

What we'd like to do is moving tapes offsite.
Trying to do this with the corresponding commands
(checkout libv, move drm) gets very ugly results.
A checked out volume gets the status "out of  library",
but after verifiying the tape-header the robot doesn't take it
out of the DLT4000 drive and the drive's led switches to green.
Querying the status shows no tape in the drive. But the next
backup fails when trying to put another tape in.

There are new lines in the error-report like this:

4225DB66   0325131898 T H lb0            OPERATOR INTERVENTION REQUIRED
5680E405   0326201198 P H mt3            STORAGE SUBSYSTEM FAILURE
0BA49C99   0324175798 T H vscsi5         SCSI BUS ERROR

The whole library/control/system hangs up! Tapes cannot be moved for
example
with the <dismount vol> - command and I have to restart the adsm-server and

initialise the STK-library to get back to normal business.

All other operations during our daily backups are working fine.