Is there food stuck?
It is possible that the Feed Tube Pusher can become wedged in the Feed Tube. Often times it is something as simple as a piece of food has lodged between the Feed Tube and Feed Tube Pusher.
To Remove the Feed Tube Pusher: Soak the Work Bowl cover in warm water, or wash in the top rack of Dishwasher. This will warm and soften the pusher, making it easier to remove.