Why can i not invite any1 on my ps3 during online cod4 ?

I've read other posts saying that the NAT Type should be 2 and stuff like that and it is and my friends also are Type 2, so i cannot figure out why i can not invite any1 or sometimes get invited into parties. I have a Belkin Router wireless ... if anyone can explain to me how to fix this, i'd appreciate it a lot! Thanks !
Why can i not invite any1 on my ps3 during online cod4 ?
Yea this happened to me also and still does. Make sure when they invite you they aren't in a game they have to be in a lobby. I make my friend do that so it works 100% of the time for me at least. When I try to enter in a game that my friend is in it is highly impossible that I won't get in
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