Friend can't connect to my Co=op multiplayer server

[Domethiuos]

I've searched here and the web and can't find a resolution to this. I created a mission setup a server one friend connects fine and another can't. He can download the map but gets looped out to the co=op dogfight screen constantly never gets into the server.  Has anyone had this issue and resolved it?

 

Thanks

[JimTM]

Does your friend have user mods enabled? They cannot connect if the server does not allow mods.