Sys' is undefined or ASP.NET Ajax client-side framework failed to load in a ASP .NET 4.0 website

Hello,
I am using Asp.net 4.0 and Ajax v4.0. I am using AJAXToolKit for quick search functionality..I am getting ‘Sys’ is undefined or ASP.NET Ajax client-side framework failed to load in a ASP .NET 4.0 website..When i run my appliction on local server then everything work fine but when i access my application from NLB client server then i get this error..I check both application server IIS setting, Machin.config, Web.config..all are identical..even i try to make changes in web.config file like putting handlers, etc.. but no luck. i assume in .net4.0 there no need to change in web.config as it is already taken care by Visual Studio...i gone through many blogs and tried all combination but no luck..:(..even i restall my framework on both application..rebooted many times...pls let me know if you can help me..fast response is appriciated..thanks
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