Ajax Tookit Not Working After Upgradation from 3.5 to 4.0

I Have a website developed in .net 3.5 and now I I Have updated  same site in 4.0
(by opening in VS 2010)

all buisinessLogic and code working fine, but Ajax is not Working in website after update in to 4.0.

I tried to Use new Toolkit i.e. AjaxControlToolkit .NET 4 and replaced Standard ScriptManager to ToolkitScriptManager

I also Deleted my web.config and re configured but still no success. :(

Same Toolkit Works with fresh new Site but not in Existing site.

Please Help me .. How I can resolve this problem.

Thanks in Advance.



...