Unable to play premade coop with friend.

Every time I click on "Start Mission" and then select my friend it will die out a little bit after it start loading the map.  It then shows us both that we are in a game with each other but we're not.  Also, we are unable to start a new one.  Relogging does not help at all.  We have to join another game for awhile and then leave to see if it is gone yet... only to have it happen again.  Any help?