Well, please bear in mind that the game doesn't use the Steam connectivity stuff at all, so if you're getting a "no ping response" message in some part of Steam, that's definitely indicating that there is a problem with more than just Tidalis connecting the two of you -- those are two completely different products there.
It's possible that if you have an unusual setup with your DMZ, that your ip is being reported incorrectly to the server lobby, I'm not sure. You could have AcidWeb tell you what your public ip is showing up as, and compare that to what you think the value should be. And if that doesn't match, he can direct-connect to your ip that actually should be used.
The connection from the client to the host is absolutely identical to the one used in AI War, it's even the same Lidgren network library. It's a single UDP port, and the only difference is that the port is 1 higher than the port used in AI War. If you think that the game itself is doing something wrong, you could always try having the client do a telnet into the host on the port that you're using and see if that succeeds in connecting or what the message is. If it's not connecting, then the IP must be wrong, or some sort of filtering or blocking is going on on one of the two ends, at any rate.
What message is it giving you when it fails, and is it logging anything in the RuntimeData folder on either of your computers? It's possible that you might be running into some sort of non-English-OS parsing error or something that we'll need to fix, but that would show up as an error log. I'm not aware of any such issues with Tidalis, but it's happened to us in the past and we don't have any non-English-OS computers to test with, so that could be related.
