Thanks, D3D for your bug report.

It works over the internet here, so I need some more information. Are you using the demo projects client.c and server.c, or have you written something from scratch? Could you debug into this and see where exactly it crashes(this is important for me to even start the search)? It seems your computers are on a local network. Could you try to connect to the external IP (or loopback address?) and forward to different computers for both ports?