Problems with JavaScript

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Joel I am getting this message when I click on the link to execute the 
changeForm code:LIne 0 Error, Object Expected. Here is my code:


<script language="javascript">
var useridCookie = "useridCookie";
// GetCookie() will return the data that is contained //
// in the cookie specified by the name pass in.       //

function GetCookie(name) {
  var value = name + "=";
  var i = 0;
  while (i < document.cookie.length) {
    var j = (i + value.length);
    if (document.cookie.substring(i,j) == value) {
       var len = document.cookie.indexOf(";",j);
    if (len == -1)
          len = document.cookie.length;
    return unescape(document.cookie.substring(j, len));
    }
    i = document.cookie.indexOf(" ", i) + 1;
    if (i == 0) break;
  }
  return null;
}
function changeForm() {
 GetCookie(useridCookie);
 document.useridform.USERID.value = cookieValue;
 document.useridform.submit()
}
</script>



Here is my form:


<form name="useridform" method=GET action=/cgi-bin/iteminq>
 <input type="hidden" name="XCAT" value="ACC">
 <input type="hidden" name="USERID" value="GUEST">
 </form>


Here is my a href code:

<td height="11"><a href="javascript:changeForm()" target="mainFrame"><img 
src="Images/Clip%20Art/Accessories%20Button.gif" width="118" height="26" 
border="0"></a></td>

Thanks,

Justin Houchin
Programmer
Reliatek, Inc
jhouchin9@charter.net