Hi
Here is the simple steps to configure this control
Step 1: Take a ScriptManager ajax control
step 2: Take a ModalPopupExtender ajax control
Step 3:Configure the ModalPopupExtender like this
<cc1:ModalPopupExtender
ID=”ModalPopUpExtender”
runat=”server”
TargetControlID=”Button”
PopupControlID=”Panel1″
CancelControlID=”btnCancel” />
The complete asp.net html page is like this
<%@ Page Language=”C#” AutoEventWireup=”true” CodeFile=”ModalPopUp.aspx.cs” Inherits=”ModalPopUp” %>
<%@ Register assembly=”AjaxControlToolkit” namespace=”AjaxControlToolkit” tagprefix=”cc1″ %>
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
<html xmlns=”http://www.w3.org/1999/xhtml”>
<head runat=”server”>
<title></title>
</head>
<body>
<form id=”form1″ runat=”server”>
<div><asp:ScriptManager ID=”ScriptManager1″ runat=”server”/>
<cc1:ModalPopupExtender
ID=”ModalPopUpExtender”
runat=”server”
TargetControlID=”Button”
PopupControlID=”Panel1″
CancelControlID=”btnCancel” /><asp:Button
ID=”Button”
runat=”server”
Text=”Click Here”
onclick=”Button_Click” /><asp:Panel ID=”Panel1″
runat=”server”
Height=”100px”
Width=”125px”
BorderColor=”blue”
BorderWidth=”10px”><asp:RadioButtonList
ID=”RadioButtonList1″
runat=”server”><asp:ListItem Value=”1″>Asp.net</asp:ListItem>
<asp:ListItem Value=”2″>C#</asp:ListItem>
<asp:ListItem Value=”3″>SQL Server</asp:ListItem>
</asp:RadioButtonList>
<asp:Button
ID=”btnCancel”
runat=”server”
Text=”Cancel” /></asp:Panel>
</div>
</form>
</body>
</html>
Now Compile the page. You will see page like this
Chandradev's Blog 
what is this namespace in register tag?
Hi,
If you will drag and drop this control then that namespace will come. so no need to bother about this.
really nice sir …
you can try another example of it here this is also very helpful…
http://www.alltechmantra.com/2013/12/how-to-use-pop-up-control-in-asp.net.html
Hey very nice blog!
Thanks.