Spring RTS Engine

when i try to host for more than 3 persons 1 of them doesn't connect in the game. im behind a router firewall (configured to allow the default port for hosting spring) also i set up NAT (hopefully correctly) did any1 had the same problem?? or anybody knows what to do? i dont want to plug off the router because i have a LAN at home and friends come to play spring.
if anyone has any idea to fix the problem post here.
id really apreciate some help.

Are any of you using large number of connections? (Torretns, emule etc..?) Some NATs have limited number of entries and torrents can quickly use them all...

Licho i updated the router's firmware and everything seems to be ok.
3/3 games i hosted were fine lets hope i wont have any more problems.
thanks for your time