Anyone else having this problem? My friend and I have been playing weeks now without a problem, but when I select online play tonight, it just comes back saying it failed to initialize online play. Some kind of server down?

Same. Not sure what happened.

It did eventually start working again. Just a temporary glitch for us anyway. We managed to finish the game.

When I started playing coop it worked but now it never does. I have tried hosting games for my brother and joining my brother's games repeatedly and it never works.

What keeps happening is that after accepting the invite, we end up in a game alone without the other person. The person hosting the game never sees the person they invited show up.

Same here, just stuck on "Initializing Online Play"
The game never resolves or times-out.

One time it did time-out and I was presented with Host/Join screen, but I can't even get that anymore.