Sys is undefined

Question

I fixed my problem by moving the <script type="text/javascript"></script> block containing the Sys.* calls lower down (to the last item before the close of the body's <asp:Content/> section) in the HTML on the page. I originally had my the script block in the HEAD <asp:Content/> section of my page. I was working inside a page that had a MasterPageFile. Hope this helps someone out.

When I experienced the errors

• Sys is undefined
• ASP.NET Ajax client-side framework failed to load

in IE when using ASP.NET Ajax controls in .NET 2.0, I needed to add the following to the web.config file within the <system.web> tags:

<httpHandlers>
  <remove verb="*" path="*.asmx"/>
  <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
  <add verb="GET" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler" validate="false"/>
</httpHandlers>

Try setting your ScriptManager to this.

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true" /> 

Dean L's answer, https://stackoverflow.com/a/1718513/292060 worked for me, since my call to Sys was also too early. Since I'm using jQuery, instead of moving it down, I put the script inside a document.ready call:

$(document).ready(function () {
  Sys. calls here
});

This seems to be late enough that Sys is available.