In ASP.net 2.0, it is using XHML page instead of HTML page. The XHTML page must be a well-formed and valid XML document. The default is XHTML DOCTYPE <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" " http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd