explanation by W3 is: "You have used the attribute named above in your document, but the document type you are using does not support that attribute for this element. This error is often caused by incorrect use of the "Strict" document type with a document that uses frames (e.g. you must use the "Transitional" document type to get the "target" attribute)"
ive read the satay method and most of the code can indeed be stripped. however, to make it validate 100% i need to alter the flash code which im not able to do, its a free image viewing tool and the maker has prevented people from opening it. perhaps ill point him to this thread and the satay method