Ran into an error in IE6 on a site I was developing:
"Attribute only valid on v:image"
The error message popped up on a Google Map canvas I had embedded in the page whenever a user interacted with the map.
The culprit was a combination of DD_belatedpng and a rule included by default in html5boilerplate where all tags were being fixed by DD_belatedpng when the page loaded. Removing the img selector from this rule resolved the error.