So, what you are saying is that the btnAddUser_Click event is not firing though you have clicked the button.
Is the page_load firing when you click the button? If answer is No, you have a problem with class name.
public partial class testsample: System.Web.UI.Page
<![CDATA[<%@ Page Language="C#" AutoEventWireup="true" CodeFile="testsample.aspx.cs" Inherits="testsample" %>]]>
So the testsample must match so that the right class is invoked. This is sometimes a problem coping code with duplicate name.
Ok, now if your page_load fires, check
Page.IsPostBack
It should be true when you clicked the button.
Debug your code and see, if there is any Response.End or anaything which obstructs to go into the button_click event code.
Hope your problem will be solved.
cheers