Spring RTS Engine

So, me and my friends decided to try and play Spring again. We usually don't play online, only against each other, and I usually have to host. However, since I got a new computer, I have not been able to successfully host a game (none of them can connect). I've tried forwarding ports, not forwarding ports, turning off my firewall, keeping the firewall on, etc, but they still cannot connect. They have the same problems when they host. What can I do to remedy the problem?

Any help would be appreciated.

P.S.- I'm not entirely sure that I forwarded the ports right, the tutorial in the FAQ is kind of vague.

if you're a bit into deep computer magic, use wireshark. if not, well, there's probably some firewall that you don't know about...

Does someone of you have multiple network interfaces or multiple IPs on a single network interface? I remember I had similar problems and it seemed spring used the wrong NIC/IP... At least it worked after I removed my second IP from my (single) network interface.