AsyncFileUpload control not showing proper error message

Hello,

I have below code for AsyncFileUpload control in one page.

<asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><cc1:asyncfileupload onclientuploaderror="uploadError" onclientuploadcomplete="uploadComplete"
                        runat="server" id="AsyncFileUpload1" width="242px" completebackcolor="White"
                        uploadingbackcolor="#CCFFFF" throbberid="imgLoader" onuploadedcomplete="FileUploadComplete"
                        uploaderstyle="Modern" clientidmode="AutoID" />&nbsp;<asp:Image ID="imgLoader" runat="server" ImageUrl="~/Images/ColumnProgress.gif" Style="margin-bottom: 0px" /><br /><asp:Label ID="Label1" runat="server" CssClass="Errortext" Text = ""  /></ContentTemplate></asp:UpdatePanel>

Below is the script code to generate the error message.

<script type="text/javascript">
        function uploadComplete(sender) {
            debugger;$get("<%=Label1.ClientID%>").style.color = "green";$get("<%=Label1.ClientID%>").innerHTML = "File Uploaded Successfully";
            document.getElementById("Label1").innerHTML = "error";
           // window.opener.location.href = window.opener.location.href;
           // window.opener.location.reload(true);
            //window.close();
        }
        function uploadError(sender, args) {
            debugger;$get("<%=Label1.ClientID%>").style.color = "red";
          //$get("<%=Label1.ClientID%>").innerHTML = "File upload failed. Please check file format or size.";$get("<%=Label1.ClientID%>").innerHTML = args._errorMessage.replace("Server Response Error: ", "");
        }

Now, I know that whenever we throw an exception from the code behind with proper error message, ajax control will ask for that annoying error popup. 'Do you want to see response page' .. I wanted to skip that. So I wrote below code in Global.ascx file to supress the error response.

  protected void Application_Error()
        {
            Exception ex = Server.GetLastError();
            if (ex.InnerException != null && Request.Url.Query.Contains("AsyncFileUpload1"))
            {
                // This error is generated by a AsyncFileUpload postback.
                Response.Close();   // Close the response
            }
        }

It is not giving me that error pop up, but everytime shows below error message instead of my custom error message which is thrown by exception.

Error Message  :  The requested file uploading problem.

Can anyone please help me to show my custom error message?