Sounds like an output sensor. Is it reporting a "Paper Jam" or "Wrong Paper Size?"
As the paper journeys through the printer, there are sensors that pick up the leading edge of the paper. If the printer doesn't see the sensor being tripped within x milliseconds of the previous sensor, it assumes that there is a problem; either the paper has jammed or the wrong paper size was inserted. Either way, the printer will stop.
The upside to this, however, is that those switches are usually optical sensors; either the switch slips out of its holder, or the optical sensors have dust in them; a good cleaning and blow out all the sensors with compressed air will often fix the problem.
--Greg