'document.f1.button' 为空或不是对象

以下是我的代码.请各位帮忙看看.感激不尽!
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html>
<head>
<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="Content-Type" content="text/html; charset=euc-jp">
<meta http-equiv="Content-Script-Type" content="text/javascript">
<link href="css/styles.css" rel="stylesheet" type="text/css">
<script language="JavaScript" src="applier.js"></script>
<script language="JavaScript" src="xCubeDb.js"></script>
<script language="JavaScript">
<?tag xCubeData ?>
</script>
<script language="JavaScript" src="scripts/common.js"></script>
<script language="JavaScript" src="scripts/title.js"></script><SCRIPT LANGUAGE="JavaScript">
<!--
function backup(){
document.f1.button.value="backup";
//button_not();
document.f1.action="pbx.cgi";
document.f1.enctype="";
document.f1.submit();
}
function Result(ext, ip, str)
{
this.ext = ext;
this.ip = ip;
this.str = str;
}var ResultTable = [
<?tag results ?>
];function loader()
{
applyInfo("1", ResultTable, document);
}-->
</SCRIPT></head><body onload="loader();">
<script language="JavaScript"><!--
site();
// --></script>
<form name="f1" method="POST" onsubmit="return false">
<table WIDTH="100%">
<tr><td class="ttl" NOWRAP>排厦怠极瓢肋年∈ＳＡＸＡ∷</td></tr>
<tr><td class="txt">　</td></tr>
</table>
<table WIDTH="100%">
<tr> 
<td  NOWRAP WIDTH="65%">
<script language="JavaScript">
<!--
help_view('help000');
-->
</script>
</td>
<td NOWRAP class="values">
<SCRIPT LANGUAGE="JavaScript">
<!--
input_botton_middle('button3_middle','backup();','','backup');
-->
</SCRIPT>
</td>
</tr>
</table>
</form>
</body>
<head>
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Expires" CONTENT="Thu, 01 Dec 1994 16:00:00 GMT">
<META HTTP-EQUIV="Cache-Control" CONTENT="no-cache">
</head>
</html>