Uncaught TypeError - Cannot Read Property ID Of Undefined

I am using RadAsyncUpload which is defined like this

Code:
<telerik:RadAsyncUpload ID="FileUpload1" runat="server" Skin="Forest" Width="272px">
</telerik:RadAsyncUpload>

And I have a asp.net button defined like this

Code:
<asp:Button ID="btnUpload" Width="180px" Height="30px" runat="server" Text="Upload"
onclick="btnUpload_Click" />

Now it works and it uploads the file , but now i want to have a Progress Bar , so like other controls i did the following

Code:
<telerik:AjaxSetting AjaxControlID="btnUpload">
<UpdatedControls>
<telerik:AjaxUpdatedControl ControlID="btnUpload" LoadingPanelID="RadAjaxLoadingPanel1"></telerik:AjaxUpdatedControl>

[Code] ....

If I add this Ajax code , my Upload does not work , it give me the Following Error

Code:
Uncaught TypeError: Cannot read property 'id' of undefined

And chrome gives more info like

Code:
Uncaught TypeError: Cannot read property 'id' of undefined Telerik.Web.UI.WebResource.axd:2889
Telerik.Web.UI.RadAjaxControl._initializeRequest Telerik.Web.UI.WebResource.axd:2889
H.z.callBaseMethod Telerik.Web.UI.WebResource.axd:3

[Code] .....