sharp ar-160 single document feeder question

I have the Sharp AR-160 copy machine with their Single Pass Document
Feeder.
When inserting an original paper into the feeder, the motor starts, but
the paper does not move, the motor stops and the error message "E7"
appears on the copiers small lcd screen.

Does anyone know what E7 means and what the problem is and what if
anything I can do to alleviate the problem?

Aaron

PS:  if this is not the correct group for this topic, please suggest
where it should be posted.