Debug JavaScript/VBScript in ASP.NET Applications

...To verify that Internet Explorer is set up correctly, open Internet Explorer, choose Tools | Internet Options. Click the Advanced tab and find Disable script debugging about halfway down the list. Make sure there is no check in the box next to this option. Click OK and close Internet Explorer. The browser is now ready to work with Visual Studio .NET to debug your application...
http://devcenter.infragistics.com/Articles/ArticleTemplate.Aspx?ArticleID=2183