[Konstantin Katsovich]

Вы не посылаете ID Вы посылаете [object]
Попробуй вот так

 
var id = crmForm.all.parentcustomerid.DataValue[0].id;;
 
// Prepare the SOAP message.
var xml = "<?xml version='1.0' encoding='utf-8'?>"+ 
"<soap:Envelope xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'"+
" xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'"+
" xmlns:xsd='http://www.w3.org/2001/XMLSchema'>"+ 
GenerateAuthenticationHeader()+
"<soap:Body>"+ 
"<Update xmlns='http://schemas.microsoft.com/crm/2007/WebServices'>"+ 
"<entity xsi:type='account'>"+ 
"<acc_ceoid>"+crmForm.ObjectId+"</acc_ceoid>"+ 
"<contactid>"+id+"</contactid>"+ 
"</entity>"+ 
"</Update>"+ 
"</soap:Body>"+ 
"</soap:Envelope>";
// Prepare the xmlHttpObject and send the request.
var xHReq = new ActiveXObject("Msxml2.XMLHTTP");
xHReq.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
xHReq.setRequestHeader("SOAPAction","http://schemas.microsoft.com/crm/2007/WebServices/Update");
xHReq.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
xHReq.setRequestHeader("Content-Length", xml.length);
xHReq.send(xml);
// Capture the result
var resultXml = xHReq.responseXML;