Keep trying. Do as Alphascrab said and have the Scrab walk towards you. Make sure he is facing you when you run off the ledge. It takes the Scrab some time to turn around and face you after you just ran past him. By the time he starts running after you, you should already be grabbing the ledge and hoisting up in the nick of time. You need to just run off the ledge and after you hit the ground, still running by the way, you need to jump while you're running and whilst in the air, hold the up button so by the time you grab onto the ledge, you're allready hoisting up. Sounds very complicated, but once you get it, it's very easy.
-oddguy
