yea i have been having this problem since the newest PSN update the other day, you can't join sessions via Party chat right now either unless you have a digital copy of the game or got lucky i guess. because anytime i want to join a fire team right now the only way i can is if i add the person and join via the roster next to the inventory page. hopefully this will be fixed soon it's really just the tools that were in place to join fireteams are no longer in sync with the tools that sony has to provide, and Sony won't fix it the game will have to in the next update.