I'm reading it's still troublesome.
I realize that the PSN just came back from a month outage, but this problem affected me before and after the outage. A friend and I cannot get invites to work. To the best of my knowledge both of us can accept other invites just nothing from each other. We end up with a message along the lines of "game session is no longer available". Mind you this really just hurt us being in a party for something like TDM and we are mainly playing FFA now, but when we get to an empty FFA server, we still can't answer the invite. Hitting "join" works though, but again it all renders a party impossible. What could be causing this and how can we fix it? Just wondering if it has to do with anything router related, possibly the NAT type?