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Error “‘Sys’ is undefined” in Asp.Net Ajax

Posted by triaslama on November 29, 2008

When I try ASP.NET Ajax in my development server I get this Javascript error: “‘Sys’ is undefined“. This error occur because I place <asp:ScriptManager runat=”server” /> element in my page.

Wondering why, I search in internet and hope that I will find one of the solution. After several trial and error finally I can find the solution and it work just fine for me.

To solve the error we need to modify web.config file, add the following under <system.web />

<add  verb=”GET,HEAD” path=”ScriptResource.axd” type=”System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35″ />

Nothing more I can say, but if you get the same error when you work with ASP.NET Ajax try the above solution, and I hope this help.


14 Responses to “Error “‘Sys’ is undefined” in Asp.Net Ajax”

  1. DotNetURL said


    Nice blog..publish you new content url at and get reader and back link form us for free

  2. Danny said


    This solved my problem! Thank You very much for this post 🙂

  3. my said

    Excellent! I looked at several forumns, which suggested changing lots in the web.config files and which I didn’t want to do. I tried your and VIOLA! it works like a charm. Thank you.

  4. jcentauri said

    Indeed useful. Thanks!

  5. Samir said

    Thanks…!! it works for me

  6. I should email you about it.

  7. shijobaby said

  8. chart said

    hoo good


  9. Hi,
    It works for me. Thanks!!!!

  10. TimWillDoIt said

    This hasn’t worked for me yet. I’ve found the same (or similar) solutions all over the Internet. But none of them have helped me. My web.config has all the right lines in all the right places.

    This works when I “view in a browser” inside VS2005 but when I copy the files up to the web host server, I get the error, “‘Sys’ is undefined“. It’s a totally blank page with nothing in it but the scriptmanager.

    Can someone help me with an explanation why this would work locally but not on the web server. And please don’t tell me that it’s probably the web server because I have no control over that. Thanks.

  11. bijesh said

    thanks man keep u r helping mind

  12. rahul said

    Thank you very much.Its really helpful

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