Mission file not found, Help!

[Dale, Table Technician]

I have been trying to connect to a friend of mine to play Civil War but everytime the map loads it comes up with an error saying that the mission file couldnt be found. He can join mine no problem. My friend said that he had Operation Arrowhead but un-installed it and had a DayZ mod but he's not sure if that's un-installed. Any idea whats going on?