in case anyone is interested here is the official canon.com reply (after I replaced my printer btw):
Dear Customer,
Thank you for your recent enquiry regarding your Canon product.
In response to your query, please be advised that the error code "5010" indicates there is a scanner error and...
just bought a canon mp-510, did everything as said in the manual,
and the lcd screen says "error code 5010". Couldn't find any definition or clarification for what it means, please help.