TripleA can not connect to the internet well if you are behind a proxy. That is probably what is stopping him.
You can still do PBEM and PBF (i think), but only if your dice roller is either the internal one, or can get through the proxy.
And you can definitely still play locally (and manually email or post the savegame if you want).
But i do know that you can’t connect to the lobby from behind a proxy.
Unless you know how to configure your proxy and/or triplea to work together, then you are out of luck.
Don’t ask me how, my knowledge only extends to knowing how to host.
I hope to get a network engineer or someone to code some proxy support for us one day.