her er svaret - det står lige under fejlbeskeden:
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), or by using vendor proprietary extensions such as "marginheight" (this is usually fixed by using CSS to achieve the desired effect instead).
Så kigger man på den fundne doctype:
Errors found while checking this document as HTML 3.2!
og så begynder man at forstå sammenhængen.
Vi er på vej til HTML 5 - HTML 3.2 er en dødsejler...