unreal tournament 3 for xbox 360

[usmc071984]

so heres my deal guys. any time i try to play this game aside from single player mode, it gives me this message.

Error
Your network configuration is not compatable with hosting matches. Please check your router's manual for instructions on setting up 'port forwarding' or a 'dmz server'.

can anyone explain/ help with this issue? this is the only game ive ever had a problem like this with on my 360. everything else plays online perfectly!