Usually a printer failure. Very common if used near cooking areas where grease builds up in the printer. You need to get a dealer to test the printer.
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If anyone needs a Sharp XE-A102 programming manual, one of the users has it here:
http://the-checkout-tech.com/manuals/cashregisters/Sharp_XE-A102_operating_and_programming_manual.html
Registerman, January 2014