Listen Server Problems

[Fa11ure]

Hello, when playing KF with my mates i have normally always made a listen server, which has been running smoothly without problems, but now my mates try to join, sometimes it wont even respond and sometimes he will be able to join and THEN he gets DC and cant rejoin, seriously KF has never been working 100% when it comes to servers.
Help anyone?

 

[Nekomancer]

Never had any problems with my Listen server, which ports do you forward, which router model do you have and do you have a static LAN IP or do you use DHCP?