If this unit uses and optical registration, the lens on the sensor is dirty. I have to clean mine every couple of months or so.
send the unit down for a cleaning.
Turn off the machine and unplug it.
Dampen a paper towel with rubbing alcohol and clean the lens. You should get some black ink and debris on the towel.
Hit it with some canned air to make sure the area is dry. (if it's still wet when you turn on the machine, you'll dry the sensor.)
Reboot the machine and it will go back to the parking side.
If is machine uses the rollers to verify width, make sure you have them in the right position like ciber said.