stucked in "Airfield escape"

What you need to do is this: First, go to the building where you are supposed to get the valve handel. If you stand next to the big hill, and look around, you will see two doors (one on the left, which leads to the valve handel, and one on the right). Take the door on the right. You will know it is the correct way if you enter the door and immediately come to a flight of RED stairs. follow the stairs up, all the way up. Do not be afraid to enter the room. when the General (older guy, lighter blue uniform than the other guy) has stopped pacing, walm up behind him and press X. You will pick his pockets, and receive the truck key.