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As you already know this is caused by remaining paper stuck inside your printer, or a dirty/defective jam sensor. Follow the directions from the link below and any visible paper from the areas instructed (click the link below:http://files.support.epson.com/htmldocs/wf520_/wf520_00ug/wwhelp/wwhimpl/common/html/wwhelp.htm?context=Epson&file=problems.11.9.html#1483034After your done doing that then remove all cartridges and power off the printer > Check in the print head area for any tiny pieces of paper. For the best results use compressed air to remove all dust from the internals of the printer > Blow the paper feed 3-4 times .
Often times it is something so small its hard to see.When done with that then re-install all cartridges and power on the printer and get back to me with the results please.