Sys is undefined

I have an ASP.Net/AJAX control kit project that i am working on. 80% of the time there is no problem. The page runs as it should. If you refresh the page it will sometimes show a javascript error "Sys is undefined".

It doesn't happen all the time, but it is reproducible. When it happens, the user has to shut down their browser and reopen the page.

This leads me to believe that it could be an IIS setting.

Another note. I looked at the page source both when I get the error, and when not. When the page throws errors the following code is missing:

<script src="/ScriptResource.axd?d=EAvfjPfYejDh0Z2Zq5zTR_TXqL0DgVcj_h1wz8cst6uXazNiprV1LnAGq3uL8N2vRbpXu46VsAMFGSgpfovx9_cO8tpy2so6Qm_0HXVGg_Y1&amp;t=baeb8cc" type="text/javascript"></script>
<script type="text/javascript">
//<![CDATA[
if (typeof(Sys) === 'undefined') throw new Error('ASP.NET Ajax client-side framework failed to load.');
//]]>
</script>

Solution 1:

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.

Solution 2:

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>