js高手帮忙看一下，为什么运行后报错 text1未定义？谢谢

下面代码运行后提示text1未定义~~~~~可是text1已经定义过了呀~~
<%@ Page language="c#" Codebehind="WebForm1.aspx.cs" AutoEventWireup="false" Inherits="WebApplication2.WebForm1" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>WebForm1</title>
<meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
<meta name="CODE_LANGUAGE" Content="C#">
<meta name="vs_defaultClientScript" content="JavaScript">
<meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
<script language=javascript>
function OnMoveText()
{
var x,y;
var stext;
x=window.event.x;
y=window.event.y;
div1.style.left=x;
div1.style.top=y;
div1.style.display="block";

stext=text1.value;
div1.innerText=stext;

}
function OnMoveOutText()
{
div1.style.display="none";
}
</script>
</HEAD>
<body MS_POSITIONING="GridLayout">
<form id="Form1" method="post" runat="server">
<asp:DropDownList id="DropDownList1" style="Z-INDEX: 101; LEFT: 328px; POSITION: absolute; TOP: 96px"
runat="server" Width="184px" Enabled="False">
<asp:ListItem Value="123" Selected="True">123</asp:ListItem>
</asp:DropDownList>
<asp:Button id="Button1" style="Z-INDEX: 102; LEFT: 384px; POSITION: absolute; TOP: 152px" runat="server"
Text="Button"></asp:Button>
<div id="div1" style="POSITION: absolute">
</div>
<input type=text id="text1" value="测试" onmouseover="OnMoveText()" onmouseout="OnMoveOutText()">

</form>
</body>
</HTML>