The css and xhtml had some problems that prevented the validation:
- unescaped "&" entities
- the css used for the lightbox contained invalid css hacks
- escaped "&"
- wrote 2 separate css sheets for ie and other browsers, deleted the hacks for transparent background in lightbox by using a png back image (for browsers supporting png alpha transparency); for ie there is no other way that to use "filter" and "opacity" hacks.