When i go connect to a MP game it works fine, it takes along time but i end up connecting with other players

heres the problem,

When i try to invite/join a GOW 2 MP with sum1 off my friends list, it doesnt connect. Tells me "Cannot connect to host".

I tried a different game and it worked, but does not work for GOW 2


Any suggestions???
I did port forward the necessary ports provided through Xbox live
I used DMX
I Restarted the router/modem (power cycle)
I did the little tricks xbox live told me ( xx lb rb xx )
Connection to everything is Confirmed
NAT is open



Xbox live cant even help me, maybe its a game problem?