ajax loader c#

Page:

<%@ Page Title="" Language="C#" MasterPageFile="~/RoseindiaMaster.master" AutoEventWireup="true"
CodeFile="UpdateProgress.aspx.cs" Inherits="UpdateProgress" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
<div>
<h2 style="color: Green">
UpdateProgress in ASP.NET 4, C#</h2>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1">
<ProgressTemplate>
<img alt="" src="Images/Preloader.gif"/>
</ProgressTemplate>
</asp:UpdateProgress>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<br />
<asp:Button runat="server" ID="load_Button" Text="Load Data" OnClick="load_Button_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</div>
</asp:Content>

cs page: 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Threading;
public partial class UpdateProgress : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void load_Button_Click(object sender, EventArgs e)
{
Thread.Sleep(50000);
}
}

credit: http://www.devmanuals.com/tutorials/ms/aspdotnet/updateprogress.html