关于atlas和母版页冲突的问题....

我刚发现利用Atlas实现无刷新，只要有母版页就不好使，谁知道为什么？我的代码MasterPage.master<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="a_MasterPage" %><!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>无标题页</title>
</head>
<body>
    <div>
        <asp:contentplaceholder id="ContentPlaceHolder1" runat="server">
        </asp:contentplaceholder>
    </div>
</body>
</html>
1.aspx<%@ Page Language="C#" MasterPageFile="MasterPage.master" AutoEventWireup="true" CodeFile="1.aspx.cs" Inherits="a_1" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">        <form id="form1" runat="server">
        <atlas:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering=true />
        <atlas:UpdatePanel runat="server"  ID="UpdatePanel1" Mode="Conditional">
        <ContentTemplate>
         <asp:Label ID="PartialPostBackLabel" runat="server"  />
        <asp:Button ID="PartialPostBackButton" runat="server" Text="页面 部分进行回发" OnClick="PartialPostBackButton_OnClick" />
        </ContentTemplate>
        </atlas:UpdatePanel> 
            
    </form>
    
</asp:Content>
1.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;public partial class a_1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {    }    protected void PartialPostBackButton_OnClick(object sender, EventArgs e)
    {
        PartialPostBackLabel.Text = DateTime.Now.ToString();
    }
}