This is a very recent problem...up until a few days ago my friend and I could connect to each other's parties or chat sessions no problem. Now, however, Xbox LIVE will not allow us to connect. If we try to accept each other's party invite, we get error messages saying "Cannot connect to Xbox Live party" or something like that. When we send chat invites and accept, the Xbox Live window says "Joining chat", and then after a few seconds the chat session just disappears from the chat menu.
Both of us have working internet connections, both have XBL gold, and both can connect well with others. Neither of us has any NAT errors or anything. And again, this is only recently, up until a few days ago we could connect fine. Has anyone else experienced this before, and is there a fix? This is really getting annoying.