hmm makes sense that it is a router problem. As I already said my firewalls are turned off.

what do you mean by "connects with your computer over internet"? How can I adjust that? The server uses my internet connection with a specific local ip-address (192.168.2.116) automaticly assigned by my router. Then I execute the session_connect-function on my client pc (session_connect ("test", "192.168.2.116)"). But the client cannot find a server using this ip-adress.