调试oa系统源码时出的错误,请高手指点

<%@ Page language="c#" Codebehind="VerifySignIn.aspx.cs" AutoEventWireup="false" Inherits="UDS.SubModule.Login.VertifySignIn" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>VertifySignIn</title>
<meta name="GENERATOR" Content="Microsoft Visual Studio 7.0">
<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 opennew()
{
if (parent.frames.length==0)
{
var udswin=window.open("../Index.aspx","","toolbar=yes,status=yes,resizable=yes");
udswin.moveTo(0,0);
udswin.resizeTo(window.screen.availWidth,window.screen.availHeight);

}
window.opener = null;
window.close();
} </script>
</HEAD>
提示错误:Microsoft JScript 运行时错误: 'null' 为空或不是对象