I have recently updated my pc to Windows 7 and want to play Settlers 3 with two people who are on the same network.

I have spent days trawling through thousands of posts and many people say that it is not possible to connect two pc's to one internet game because there is only one public IP address. I know this is not true because we have played this game the same way for years through various versions of windows and using various routers.

My problem is as follows:

I can host & join games
Player 1 on the lan can host & jojn games AND connect to my game
Player 2 on the same lan can host & join games AND connect to my game however, the second player will make the green synchronisation bar of player 1 appear as a red dot and we cannot start the game. (the same works the other way round, basically the latest player to arrive will knock out the first).
I can play with either of them just not both at the same time.

Thanks to Ian Harris' legendary posts, which I have referred to many times over the years, I have no problem port forwarding or with firewalls.

The setup for the LAN'd computers is as folllows:

Static IP's set to both PC's
Ports 2302 - 2349 set on PC1
Ports 2350 - 2399 set on PC2
DxPorts downloaded and in use to split the ports.
All other ports forwarded
Security Essentials Firewall configured correctly to allow everything
Disabled UPnP

I should also mention that PC1 & PC2 can play LAN games with each other without a problem. I ran netstat when both PC1 and PC2 were connected to me and that confirmed that they were connected and the correct ports were being used.

So despite my opening line stating that it can't be down to the public IP address conflicting, that appears to me to be the only thing left that could cause a problem but it doesn't make sense. Please help, it's driving me insane.