A listen server? Make sure ports are open and run from game. Make friends join via external IP rather than Steam friends list/invite.
Sorry, but i have never been able to start a listen server. It is too complicated and is frustrating. I dont want instructions or tutorials. I want to choose on screen and it works right away.
I want simple setup, like L4D. Simple is better! Always!
A more simple setup of listen server could have sold even more copies of KF? I seen several posts on Steam-forum complain about this and that several customers did not buy it cause of only this reason. Other reasons can be "old graphics" or stop playing cause of bugs/crashes, etc.. But.....of all these technical issues, i consider a simple setup of a listen server to be valuable for increased gamevalue.
PS! I only play L4D on listen server and use mutators for fun or is boring. Or i dont play L4D! Mutators like jetpack, upgrades, ammo, faster reload, spawn a minigun anywhere, lasersight, spawn more bots , etc.. Is a blast! I dont use any mutator for health, so anyone can die playing or would be boring. Godmode is booooooring!