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

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 />

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

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.