I have been trying to host a cooperative game of Darkflamewolf's Enemy Within today and someone else tried to join. But they kept getting disconnected and I was wondering if the problem was me and if I could do anything.
My windows firewall is offline
My gameports that Rebirth is referring to are open
My router firewall is offline
Is there anything else I can do or will people always keep getting disconnected when I try to host a game?

edit: Oh and I am using the latest DXX Rebirth version (version 0.57.1)