Server will not support more than one client at a time

[Jolrak]

I have tried this a couple of ways. Currently my server is just connected to a cable modem and is then routing internet to my 2nd computer. My brother is able to connect to my computer through the internet from his seperate connection behind a router, however when he is connected i cannot connect and in the world.exe screen i get a
[Net__error] 192.168.0.5:2715 recieved op_sessionrequest in established state <0>
followed by
[Net__identify] unable to identify stream from 192.168.0.5:2715 before it closed.
Now i only get these errors when my brother is connected and i try to connect from my computer on the same lan as the server. If i am connected first and then he tries to connect no errors show up but the same result is seen on the client end. We both end up getting booted back to the login screen. Game runs fine for one client, any help would be greatly appreciated.