Errors in the log file:

Failed to send fh for catalog file to tape. ret=2

(new one to me!?)

E1039 Failed to flush Tape Driver buffer - Drive or Media Failure

(this one is a good one, as it happens on verious tapes, but
ALWAYS after the same session - no matter is I move order of session during

E1058 Failed to read from media - No data detected

(also a good one, as it is after EVEYTHING was verified, wonder what data it
tries to read?)

And the bnest one here:
The merge simply did not finish, it merged 2.7 session (two full & 3/4th of
the third one)
from 13 backed up.
No error or any kind. No .bak session files files available

This is getting silly!!