As Contractor stated above, it is very common for the threaded spindle on the circumferential register to seize up. This can be confirmed very easily. Simply take off the drive side cover, remove the small pinion gear on the servo motor with a 3mm allen and the try to make a circumferential move. If the motor moves, than the motor is good and the threaded spindle is seized. If the motor does not move, than you do have a bad motor. If you do have a bad motor, do yourself a favor and get it from Heidelberg. Yes it may cost a bit more, but these motors are very reliable unlike the knockoffs.