WinGate NAT problem

[dirtchamber]

Hi all. I have WinGate (latest version) on a "server" PC, witch shares the Internet connection to 2 client PCs. Untill today everything was working fine, but now the Internet doesn't work anymore. Gatekeeper on the server PC show the NAT connection attempts from the clients, everything seems to be fine (DNS running, ENS running...), but on the client PCs I can get the Internet working only by proxy. I tried reinstalling the application, but it's the same. First, I thought it could be a switch problem, but I can't explain why it's working trough WinGate's WWW proxy and not with NAT, as it should... I didn't change anything on the server or on the client PCs since yesterday, so this is really weird.
This leads me to an ideea. Could it be possible that the ISP blocked somehow the NAT features on this LAN? It's very unlikely, as I don't see how they can do that, but it's a thought.
Please help if you can, because proxying is very limited... :( Thank you.
Update: using WinGate as a client on the two PCs seems to work (with the Winsock redirector), but I guess there are limitations here too. For example, Yahoo Messenger only connects by using Firewall with no proxy option, not directly.

[genie]

No, it's highly unlikely that your problem has anything to do with NAT - most probably it's a configuration issue. Have you checked and made sure that the adapters are marked correctly in Gatekeeper (internal/external)?

[dirtchamber]

Yes, everything is configured as it should. Even a stranger thing happened. I tried to use another computer as a WinGate server (the computer is in the same LAN, only different locations) and it's exactly the same. No direct connection, only proxy...