Ajax Controls Not working

Hi,

When i place  Ajax Controls (EX:Tabs,CalenderExtender) in my project.

Design view dont show any error.But when i run it in Browser,mozilla shows XML Parsing eror,IE shows blank page.

Scriptmanager is in the master Page.

DotNet Framework 4.0.

Works fine with ajax ModalPopUpextender .

Please provide me the solution asap.

Thanks