Ok, thanks Irad. Good to know, also for others, if they run into the same problem.

After disabling PSK Reporter, the program seems to run without crashing. I tested some Pings and 3 VMails successfully delivered. I will do some further testing, always need to wait for the propagation as there is no QSO partner nearby, but PSK reporter seems to be the problem.

I had all sounds and narrations already disabled. Didn't help.

Further testing: Vara Chat 1.3.4 runs without any problem. Probably its not the KISS connection, but something in VarAC