Today, first time I put my web page into w3c validator. Not to mention countless errors.
But, I have to two fundamental errors :
1, In web page I have
meta equiv="Content-Type" content="text/html; charset=iso-8859-1"
, but apache send out utf-8 encoding in the responding header.
2, Unencoded ampersands in URL
Link like href="q?p=welcome&id=" was failed.
According to http://www.htmlhelp.com/tools/validator/problems.html#amp
, it should be href="q?p=welcome&amp;id="
Read more at validator.w3.org/