multiplayer question

[lsr]

well, i searched the forum here but haven't really found an answer, so I will start this thread to ask it. Sorry if it was answered somewhere and I missed it.
I know there's plenty of issues with multiplayer on the ps3, but I have friends who can play each other, but I can never join their games when they send me an invite, and when I start a game, they cannot join my game.

I haven't tried disabling my firewall. Maybe that's the issue. Plus, on my network connection test, my upnp says not available. I don't know if that could be causing problems. The only other thing I can think of is we are not using the same version of the game. Last night I uninstalled the patch, but none of my friends were online at the time to test it. Any help would be appreciated. Thanks.