Correcting “ASP.NET AJAX client-side framework failed to load” error

If you’re trying to use ASP.NET AJAX features (like Script Manager or Update Panel) in your ASP.NET 3.x website and getting “ASP.NET AJAX client-side framework failed to load” error, chances are your Web.config file is missing required sections. Fastest way to correct this is to create a new ASP.NET website in Visual Studio (you can delete it afterwards) and copy missing sections from the new web.config to the one in your web site.

Update: As churawut pointed out missing .AXD mapping in IIS configuration is another common source of this error (often this is done as security hardening on the IIS).  I encountered it while researching missing images in ASP.NET charts, and found out that underlying reason was missing/corrupt .AXD mapping in IIS.

22 replies on “Correcting “ASP.NET AJAX client-side framework failed to load” error”

  1. Bless you.

    My blood pressure was going through the roof.

    I was beginning to freak.

    Lots of people were claiming that you could fix it by reinstalling .Net 3.5 SP1 (no change) downloading various components (no change) rebooting servers (no change) and sacrificing various animals to assorted deities (full moon not due for two weeks, customer deadline one week)…

    And a voice of sanity says “rebuild your Web.config”… and it was so.

  2. @PW
    Glad no animals were harmed in building this code 🙂 This error usually happens when opening .NET 2.0 app in Visual Studio 2008. Sometimes it doesn’t offer upgrading to 3.x hence keeping the original Web.config

  3. The interesting (and annoying) thing is that it did – and I accepted the upgrade.

    This looks like there might be something funny going on.

    Even with a brand new .Net 3.5 SP1 web.config, Expression Web 3 keeps saying that the Silverlight media player element needs the site to be .Net 3.5 and do I want it to upgrade? I say yes, and as soon as I click on the silverlight element again, back comes the same message.

    Most odd – but I can live with it.

    What is odder is that both expression and VS will not show the WMV files I’ve got as media content in the “Media Source” browser, and the player won’t play them if I type them by hand. I guess I need to run them through Expression Encoder first, and use the output from that? No, that’s not done it. How odd.

    Sorry, I’m rambling. Many thanks for your help, anyway.

  4. Solution found for this generic message with many solutions. Ours was that the AXD extension needed to be added to the IIS Application Extensions dialog.

    if you use .net framework more than one version please
    specify .axd execute from .net framework 2.0

  5. Yaa really its very strange, i also tried to repair .Net 3.5 SP1 but no luck.
    I just replaced my web.config file with old one which was running without any problem and the error disapeard> :p
    Thanks to All who participated in this thread

  6. Wow!! THANK YOU!! Your suggestion really solved my problem.. Been banging my head on the wall..

  7. Thank you to save my day . After number of times reinstall Dotnet frame work 3.5 SP1 not working. and i found this post working like a charm.

    Thank you!!!

  8. We tried to fix that problem since last one week, but problem was due to ScriptResource.axd and WebResource.axd. This both files were missing onto the Website path. Please paste both these files and your problem would disappear. 🙂

  9. After Lots…… of Search I have Found Correct Solution Thanks
    m Looking Fwd To Your Post

  10. Yes! The solution as indicated in paragraph 1 about did the trick!!!



  11. ISSUE AJAX Client Framework failed to load.

    Check the IIS Settings before you do anything. the above solution didn’t work for me but the below one worked for me.

    1. Under IIS in Handler Mappings look for ScriptResourceIntegrated-4.0
    2. On your right handside click edit Feature Permissions and check EXECUTE

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