Hi
I have just been grappling with this and can only comment on the findings on my machine, however I should imagine this will be your issue.
The lift motor is the nearest one to the outside at the back of the machine as you pull out tray C, unplug the assembly and remove it (three screws). It is likely that the gear on the motor is plastic, (later machines appear to be brass). Check how free the mechanism rotates, by thumbing the larger gear in contact with the motor, the motion should be smooth, but I suspect you will detect a tight spot which the machine has detected as an eror. If you then remove the motor a - further two screws - the small gear should just slide off - although it may be easier to examine on the shaft, I used a lens (my eyes aren't what they used to be since I passed 40) which revealed a hairline split running down the gear, hence altering the pitch, after marking the position of the defect, putting the motor back on the assembly and then rotating the mechanism discovered that the point it seized was at the fracture mark.
I am about to embark on a quest for a new gear, which I am hoping will resolve the issue without the need for a new motor.
Hope this helps.
Ralph Diamond - Print Solutions, December 2007