请教一个Ajax的问题！急！急！急！

我用了asp.net Ajax控件TabContainer，为什么在cs文件里面发现不了服务器端控件了啊？[size=18px]客户端代码如下[/size]：
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="AjaxControl._Default" %><%@ 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>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>
    
    </div>
    <cc1:TabContainer ID="TabContainer1" runat="server" ActiveTabIndex="3" 
        Height="264px" Width="440px" 
        onactivetabchanged="TabContainer1_ActiveTabChanged">
        <cc1:TabPanel runat="server" HeaderText="新闻资讯" ID="TabPanel1">
            <ContentTemplate>
                接下来，我们要构建这个控件库（即程序集）。右击此库工程，并点击“生成”命令以生成程序集AjaxImageButtonLib.dll，此库文件中即包含了我们的服务器控件。l
            </ContentTemplate>
        </cc1:TabPanel>
        <cc1:TabPanel ID="TabPanel2" runat="server" HeaderText="科技前沿">
            <ContentTemplate>
                <asp:Image ID="Image1" runat="server" Height="184px" 
                    ImageUrl="~/image/1228971048405.gif" Width="412px" />
            </ContentTemplate>
        </cc1:TabPanel>
        <cc1:TabPanel ID="TabPanel3" runat="server" HeaderText="时尚杂志">
            <ContentTemplate>
                <asp:Image ID="Image2" runat="server" Height="229px" 
                    ImageUrl="~/image/1230904377037.gif" Width="247px" />
            </ContentTemplate>
        </cc1:TabPanel>
        <cc1:TabPanel ID="TabPanel4" runat="server" HeaderText="显示时间">
            <HeaderTemplate>
                显示时间
            </HeaderTemplate>
            <ContentTemplate>
                <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                    <ContentTemplate>
                        <asp:Label ID="Label2" runat="server" Text="Label"></asp:Label>
                        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
                    </ContentTemplate>
                </asp:UpdatePanel>
            </ContentTemplate>
        </cc1:TabPanel>
    </cc1:TabContainer>
    <p>
        &nbsp;</p>
    </form>
    
</body>
</html>
在.cs文件里发现不了Label 和Button ，为什么啊？高手指点下，谢谢！