Thanks for your reply. Actually I tried several things over the weekend without any success though.
However, today I had a chance to try one of my clients on a different LAN. To my astonishment ICQ would not work there, either, not even on clients indigeneous to that LAN which used to be working previously. Thus, I am afraid it was not SuSEfirewall2 in the first place, but rather a change in the ICQ protocol that was introduced on exactly the same day as I upgraded my server/router (ugh!).
Now the new question is, has anyone else had the same problem using Kopete
(I got 0.11.1) and is there a solution to this problem?