This is a generic error message that doesn't tell you anything but the
obvious, that something killed the session.
Can be caused by a network error, or a timeout, or a client problem.

Look at the TSM server log.
Match up the timestamps and find the matching error message on the server
end.
That usually gives you a better idea of what is going on.

(remember to check the TIME on the client vs. time on the server and adjust
for the clocks being off)