Your ball detent is worn down or is not sticking out too far. This is the piece that keeps the paintball from rolling down the barrel. Open the right panel on the right side of the gun. It is secured by two small screws. Take it off and you will see a nipply looking thing. See if it is worn down and if it is replace it. Also, cut a small piece of paper that will fit behind the detent in between the cover. This will make it stick out more.
Here is a helpful diagram.
Also, try closing the powerfeed plug. Then, rotate it counter-clockwise until one ball drops into the chamber. Then open it a SMIDGE more. That will keep multiple balls from feeding.
Hope this helps your problem.