Resolving: ASP.NET Ajax client-side framework failed to load

Sometimes you spend hours and days in finding some errors that can be solved in a simple way.

Here was the problem:

I was using AjaxToolKit in one of our web applications, it was running great for a long time, until one day our client reported that the website is like a mess. When I checked out, I found out there was a javascript error saying: “ASP.NET Ajax client-side framework failed to load” and all the ajax controls stopped working.

I tried to look out for some solution on the net:

I tried all the provided solutions, but my situation was different. When i checked the web application on any local PC, it was working fine, but on the hosting server it failed. So I followed up every single page in the application, and at the end I noticed something:

Any web application without the file “global.asax” with AjaxToolKit was working fine without any error, so when i removed this file, everything went ok. Now if you ask me what was the main cause of this problem i would say nothing since there isn’t any convincing reason for this, but removing this file was the solution for this sudden error!!

In case you encountered such a problem, try this option it might be the solution for this error !!

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4 thoughts on “Resolving: ASP.NET Ajax client-side framework failed to load

  1. 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

    • Hello,

      These errors are weird, and no logical reason for such errors, I think your problem can be solved from the webconfig, but do u have all the service packs installed on the server. And if you can try a simple code page with the ajax without a masterpage and run it locally on the server to test it.
      Hope I can help you more.

  2. I had the same error for past two days. finally i resolved the issue. add the following items in Managed Handler in IIS.
    *.asmx
    System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35
    ScriptHandlerFactory

    *_AppService.axd
    System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35
    ScriptHandlerFactoryAppServices

    ScriptResource.axd
    System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35
    ScriptResource
    best of luck

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