if you connect over the internet, your local ip address isn't valid for the other part
he has to use the ip address standing here: http://checkip.dyndns.org/

To me it looks as if he is testing with two computers in the same private subnet.

yes I can ping the pc with the internal ip adress (192.168.2.116). The session_connect-funtction seems to work, when I use this ip address because connection is set to a value != 0. Using an other (random) ip the engine crushes because the connection-var = 0. But dplay_status doesnt change so there may be sth that prevent the client to join!

@MasterQ32: Unfortunatly, this ip doesnt work at all

edit: ye, I am in the same network!

I think your router has to support NAT loopback or something like that if you want to connect your two game sessions via IP. Just enter an empty string in the session_connect IP argument to test it locally as a LAN game and enable the IP input for other clients to connect to your server over the internet.