window.dialogArguments找不到父页面的form

<script language="jscript" type="text/jscript">
function transferValueToParentWindow()
{
   var parentWindow = window.dialogArguments;
   if (window.dialogArguments != null) 
   {
      listBoxAttendee = eval("document.SelectAttendee.ListBoxAttendee"); 
      var attendeeText = "";
      var attendeeValue = "";
      for(i=0;i<listBoxAttendee.length;i++)
      {
         attendeeText += listBoxAttendee.options[i].text + ",";
      }
      parentWindow.document.parentform.txtAttendee.value = attendeeText.substr(0,attendeeText.lastIndexOf(","));
      window.close();
   }
}  
</script>父页面有一个form
<form name="parentform" method="post" action="Categories.aspx" language="javascript" onsubmit="javascript:return WebForm_OnSubmit();" id="parentform">执行这段js后，报错说“parentWindow.document.parentform为空或不是对象”