I can't connect to or host parties or sessions while connected to Xbox Live

I can connect to Xbox live, but I cant connect to any parties or sessions of my friends, and they cant connect to any of mine either. I thought this problem might go away with time, but it's almost been a week and I am still having this problem. Again, I
am already connected to Xbox live. I just don't understand what is going on and it is really beginning to frustrate me. What do I do?

:)

 

I can't connect to a specific friend's game.

This is all of the information I came up with about this issue: We can always join Xbox Live Parties no matter what. The issue is not parties, it is only games or matches. If one of us hosts a game, the other can't connect to it. It will say session is no
longer avaible etc. The only way I can connect to his game is if someone else hosts it. It only happens with one specific friend. The only thing that changed when we stopped being able to connect to each other is that the game "Black Ops II" came out and we
both played. It isn't just my profile either or my Xbox-360. There are two consoles in my house and no profile on either have been able to connect. I think it is related to connection but no settings have been changed at all.
To sum it up, if I host a game, he can't connect. If he hosts a game, I can't connect.
We can only connect to each other's game is if another player hosts. I am the only person he can't connect to, and he is the only person I can't connect to. We always
can join parties either of us are in regardless of the host

 

Xbox One- NAT type is open, cannot connect to matches/parties?

I just bought my Xbox yesterday and I'm having the same problem except it lets me join parties and talk to my friends. But when I go to join or host a multiplayer session it says it is unavailable and I need to connect to Xbox live. My NAT is open and both
the network and multiplayer tests were successful.