So last night I tried partying up with Gkev, couldn't connect to host. He tried partying up with me, couldn't connect to host. I jumped in and out of different parties with other 30 members fine, so did he. He couldn't join my game in progress, I couldn't join his. I rebooted my xbox and I think he tried the same.
One of the oddest problems I have encountered with XBL. I know if your NAT is moderate or strict you can experience this type of behavior but mine is open and I have played with Gkev before. The fact that we could both join other parties is odd as well.
Any ideas?