Hi. It means the printer has jammed usually. Have a look in the printer to make sure you don't have a paper jam. Remove the ribbon/ ink cartridge to make sure it is not jammed. Turn power off at wall. Make sure key is on REG mode. Turn on at wall. You'll see the error again. Now press CLEAR (CL) to make the register try the printer again. If it is still faulty, you might have a damaged gear, or a motor failure and it should go in to a dealer to be stripped down.
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For anyone looking for a Sharp ER-A470 manual, there is one here:
http://the-checkout-tech.com/manuals2/cashregisters/Sharp6.php
Mark, February 2010