AjaxFileUpload "OnClientUploadError" event not firing

Hi,

I have used "AjaxFileUpload" control.

<asp:AjaxFileUpload ID="AjaxFileUpload" MaximumNumberOfFiles="1" ContextKeys="KeyHiddenField" OnUploadComplete="AjaxFileUpload_OnUploadComplete"
        OnClientUploadComplete="OnClientUploadComplete" OnClientUploadError="OnClientUploadErrorTest" runat="server" />

In code behind

protected void AjaxFileUpload_OnUploadComplete(object sender, AjaxControlToolkit.AjaxFileUploadEventArgs e)
{
// want to fire "OnClientUploadError" javascript event here explicitely.
 throw new NullReferenceException();
}

Javascript :

function OnClientUploadErrorTest(sender, args) {
  
}

OnClientUploadComplete is firing properly.

For testing i want to fire OnClientUploadError event in JavaScript for that I have explicitly thrown exception in code behind.
But it’s not firing at all.