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Sys Is Undefined Microsoft JScript Runtime Error Occurs


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When working with Telerik UI for ASP.NET AJAX, I get a Microsoft JScript runtime error that Sys is undefined.

Error Message

Microsoft JScript runtime error: 'Sys' is undefined


The possible cause for this issue is that you have added a Telerik UI for ASP.NET AJAX control but your application is not configured to use ASP.NET AJAX.


To solve this issue, follow the steps described in the Common reasons for the Sys is undefined error in ASP.NET Ajax applications blog post.

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