UpdatePanel1 "asp:listItem"的"Text"属性不属于子对象

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="CourseAdd.aspx.cs" Inherits="StudentScoreManage.StuManage.CourseAdd" %>

<!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>课程管理</title>
<link href="../Styles/sub.css" rel="stylesheet" type="text/css" />
<script type="text/javascript" src="../js/calendar.js"></script>
<style type="text/css">
.style1
{
height: 262px;
}
</style>
</head>










<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<div class="ht10"></div>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<th colspan="4" align="center" class="style1">课程添加</th>
</tr>
<tr>
<td class="colr" style="width:20%">
<span class="red">

• </span>课程代码：
  </td>
  <td class="coll" style="width:30%">
  <asp:DropDownList ID="KCDM" runat="server"
  onselectedindexchanged="KCDM_SelectedIndexChanged">
  <asp:ListItem Value="0001">请选择</asp:ListItem>
  <asp:ListItem Value="100">001</asp:ListItem>
  <asp:ListItem Value="200">002</asp:ListItem>
  </asp:DropDownList>
  </td>
  <!--
  <td class="colr" style="width:20%">
  <span class="red">
• </span>课程名称：
  </td>
  
  <td class="coll" style="width:30%">
  <asp:DropDownList ID="KCMC" runat="server"
  onselectedindexchanged="KCMC_SelectedIndexChanged">
  <asp:ListItem Value="0001">请选择</asp:ListItem>
  <asp:ListItem Value="0002">数学</asp:ListItem>
  <asp:ListItem Value="100">语文</asp:ListIem>
  <asp:ListItem Value="200">英语</asp:ListItem>
  </asp:DropDownList>
  </td>
  -->
  
  </td>
  </tr>
  <tr>
  <td class="colr" style="width:20%">
  <span class="red">
• </span>学分：
  </td>
  <td class="coll" style="width:30%">
  <asp:TextBox ID="XF" runat="Server" CssClass="TextBase" ></asp:TextBox>
  </td>
  
  <td class="colr" style="width:20%">
  <span class="red">
• </span>学年学期：
  </td>
  <td class="coll" style="width:30%">
  <asp:TextBox ID="TextBox1" runat="server" CssClass="textBase" ></asp:TextBox>
  </td>
  
  </tr>
  <tr>
  <td class="colr" style="width:20%">
  <span class="red">
• </span>课程性质：
  </td>
  <td class="coll" style="width:30%">
  <asp:TextBox ID="TextBox2" runat="server" CssClass="textBase"></asp:TextBox>
  </td>
  <td class="colr" style="width:20%">
  <span class="red">
• </span>课程说明：
  </td>
  <td class="coll" style="width:30%">
  <asp:TextBox ID="TextBox3" runat="server" CssClass="textBase"></asp:TextBox>
  </td>
  </tr>
  
  </table>
  
  <div class="btns">
  <asp:Button ID="Add" runat="server" Text="添加" CssClass="button" OnClientClick="{if
• (confirm('确定要添加课程信息？')){return true;}return false;}" />
  <asp:Button ID="AddNew" runat="server" Text="添加并新建" CssClass="button" OnClientClick="{if(confirm('确定要添加课程信息？')){return true;}return false;}" />
  <asp:Button ID="Return" runat="server" Text="返回" CssClass="button" />
  </div>
  
  </ContentTemplate>
  </asp:UpdatePanel>
  </form>
  
  
  </body>
  </html>
  这是所有的代码，劳烦大家看看