Your actual problem is not about script code, It's more on your CSS or any styling that you use to position your elements in your page. That's why ASP.NET did not generate any error message to you because you don't have any script or syntax error.

About other website that have "Invalid" CSS or HTML/XHTML, well at least they don't have any major/positioning problem
Check out our sticky thread in the CSS Forum to learn more on the CSS stuff HERE

Cheers...