document.form1.select1 为空或不是对象

<SCRIPT src="check_form_std.js"></SCRIPT>
<SCRIPT language=javascript src="Tabledata.js"></SCRIPT>
<SCRIPT language=vbscript src="Formatdata.vbs"></SCRIPT>
<script language="Javascript">
function openScript(url, width, height){
var Win = window.open(url,"openScript",'width=' + width + ',height=' + height + ',resizable=1,scrollbars=yes,menubar=no,status=yes' );
}
function openem1(txt)
{ 
var txt=txt;
openScript('../hopbuy/checkcase.asp?lotto='+txt,650,370); 
}
function openem2(txt)
{ 
var txt=txt;
openScript('../hopbuy/checkuser.asp?txtname='+txt,850,450);
}
</script>
<script language="javascript">
function changelocation(issue,lotto,ch)
{
var issue=issue;
var lotto=lotto;
var ch=ch;
window.location.href="ind_case.asp?lotto="+lotto+"&issue="+issue+"&ch="+ch;
}
</script>
.......
  
  select name="select1" onChange="javascript:changelocation(document.form1.select1.options[document.form1.select1.selectedIndex].value,<%=lotto%>,<%=ch%>)">
    <%   <option  selected="<%=rs("issue")%>"><%=rs("issue")%></option>.....  想实现,通过下拉框选择不同来调用SQL数据库的信息,从而打开不同的信息.
  但却总提示:
document.form1.select1 为空或不是对象