Does your Page Conform to xhtml ?
You can check if your page is valid by following the steps below
Note1 : You must be on the internet for the Validator to work.
Note2 : Internet Explorer with XP Service Pack2 has a problem with file uploads of local files.
Firefox does not suffer from this problem.
Even if you think you write excellent xhtml code you should validate your page with the validator. It is a sobering experience.
Common errors are