Thanks for the link to the 'entities' page - that is a really complete and useful resource.
I do have the recordset code on the page, though. I am thinking now that the error might be caused because the 'Quick Link' include page has a 'mysql_free_results' php block at the bottom of the page, so that when this appears at the bottom of the detail page as well, the browser reads two such blocks of code when it only needs one (i.e. it acts on one, then gets the same request again). Could that be why I get the error?