My friend and I haven't been able to connect to each other's games or parties for the past week or so. Naturally, we assumed it was NAT related issues at first, but both of our routers are set to open NAT. I did a lot of Googling and found a lot of people with similar issues, but nothing has worked.

So, I turn to the Giant Bomb community. Anybody have any clue what's going on here?

I have that problem too. My friend an I can connect to other people's parties, but not to a party where either of us is hosting.

There was a question relating to this on SentUAMessage I believe, I think it was something to do with certain ports not being forwarded or something similar.