AJAX fun with the dreaded 'sys is undefined' error

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AJAX fun with the dreaded 'sys is undefined' error

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If you have started to play with AJAX then you have most likely come across the dreaded 'sys is undefined' error.  I found numerous articles on how to get this working but the best ones all point to making sure you have the correct entries in your web.config.   So to summarize what I have read:

1)  Go to C:\Program Files\Microsoft ASP.NET\ASP.NET 2.0 AJAX Extensions\{your version of AJAX}

2)  Open the sample web.config file and make sure you have the same entries in your web.config

3)  If you don't then copy and paste is your friend :)

4)  See if the app works now

 Here are a couple of articles to assist if you are still having issues:

Chris Riccio's blog   http://weblogs.asp.net/chrisri/archive/2007/02/02/demystifying-sys-is-undefined.aspx

Lorin Thwaits's blog  http://geekswithblogs.net/lorint/archive/2007/03/28/110161.aspx


  • Creating 2 empty files in your .net project:



    fixed the 'sys' problem for me also, Big Thanks Tobias.

    (Visual Studio 2008, .NET 3.5, deployed to win2k3 server)

  • Thanks alot. It's solved my problem.

  • Which web.config entries exactly?

  • Thanks, this solved my problem.  :)

  • http://sysisundefined.blogspot.com/2009/08/sys-is-undefined-update-panelajax.html

  • thanks, I had forgotten the modules and handlers tags in the web.config :)

  • sys is undefined error show in Dot Net 3.5 .

    We are using Ajax Tool kit..

    Give me solution............

  • MR.Corey .

    How you created the below files



  • How it will solved in Shared Hosting?

  • Thank you Tobias. Adding ScriptResource.axd & WebResource.axd to my project resolved the error.... Thank You....

  • If your developing for the intranet and you have this error look at the zone ie is showing, bottom right ,  we have a couple of polices running that was causing this error in the trusted zone,  I canged it to local intranet and it works.


  • and this had solved it for met! Thank you!! :)

  • I am using Mvc and i don't have scriptmanager in my page and getting the same error what i need to do in this case?

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