I've had this happen a couple times with my Black Rose. If the ball is in the canon, do you hear the motor running for the rotation? If so make sure the screw attaching the motor to the base of the canon is in place. I've had mine vibrate out, essentially running the motor without actually having anything to turn. Also be wary of raising the play field with the ball in the canon. It will travel up the lower trail potentially causing the upper switch paddle to get bent. Next time the ball comes down davey jones locker, it can get stuck on that switch.
Let me know if you need any other help or tips with it, I've tinkered with mine extensively for almost the first year of having it! Love this pin!