A lot of times if there is a problem with the walking foot claw, the foot will not work properly. I run into this problem all of the time, especially with old Bernina walking feet. When you move the claw up and down, the piece on top of the sole should move as well. When the piece on top of the sole no longer moves, the dealer must go inside and oil the foot for it to work again.
If the above is not the problem, sometimes adjusting the tension on the screw on sole will solve the problem. Sometimes the walking foot sole is just screwed on to tight! Just loosen the sole screw and try again.