Here is the code I believe has the problem.  It is the original code provided in the Blog (Double Dropdown) and referenced in my previous post above.

I know how these forums sometimes don't do well with code in the text, so if this doesn't come through, email me at tim.hensler@tig.com and I will send the code directly to you. 

Thanks for your help.

//Update Case record
try{xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");}
catch(e){return false;}

xmlhttp.Open("POST",url,false);
xmlhttp.setRequestHeader("Content-Type","text/xml");
xmlhttp.setRequestHeader("soapAction","update");

var xmlUpdateCase = "<?xml version='1.0' encoding='UTF-8' ?>" +
'<soapenv:Envelope ' +
'xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" ' +
'xmlns:xsd="http://www.w3.org/2001/XMLSchema" '+
'xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">'+
'<soapenv:Header>'+
'<ns1:SessionHeader ' +
'soapenv:mustUnderstand="0" '+
'xmlns:ns1="SforceService">'+
'<ns2:sessionId' +
' xmlns:ns2="urn:enterprise.soap.sforce.com">{!API_Session_ID}'+
'</ns2:sessionId>'+
' </ns1:SessionHeader>'+
'</soapenv:Header>'+
'<soapenv:Body>' +
'<update xmlns="urn:enterprise.soap.sforce.com">'+
'<sObjects xsi:type="ns3:Case" '+
'xmlns:ns3="urn:sobject.enterprise.soap.sforce.com">'+
'<ns3:Id>{!Case_ID}' +
'</ns3:Id>'+
'<ns3:Category__c>'+Categorystr+
'</ns3:Category__c>'+
'<ns3:Sub_category__c>'+Subcategorystr+
'</ns3:Sub_category__c>'+
'</sObjects>' +
'</update>' +
'</soapenv:Body>'+
'</soapenv:Envelope>';

//alert(xmlUpdateCase);
document.write(xmlUpdateCase);

xmlhttp.Send(xmlUpdateCase);
var sq = xmlhttp.status;


if ( sq == 200){
return true;
}
else{
alert('='+sq);
return false;
}

}