RetreiveEntityById jscript for CRM 2013 not working?

Hi, I have used this jscript in CRM 2011 online to RetreiveEntityById but its not working for CRM 2013! any help to find the replacement script will be highly appreciated.

// Do not make any changes to this function
function RetrieveEntityById(prmEntityName, prmEntityId, prmEntityColumns) {

    var resultXml, errorCount, msg, xmlHttpRequest, arrayEntityColumns, xmlEntityColumns;

    arrayEntityColumns = prmEntityColumns.split(",");

    for (var i = 0; i < arrayEntityColumns.length; i++) {
        xmlEntityColumns += "<q1:Attribute>" + arrayEntityColumns[i] + "</q1:Attribute>";
    }

    var authenticationHeader = Xrm.Page.context.getAuthenticationHeader();

    //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'>" +
    authenticationHeader +"<soap:Body>" +"<Retrieve xmlns='http://schemas.microsoft.com/crm/2007/WebServices'>" +"<entityName>" + prmEntityName + "</entityName>" +"<id>" + prmEntityId + "</id>" +"<columnSet xmlns:q1='http://schemas.microsoft.com/crm/2006/Query' xsi:type='q1:ColumnSet'>" +"<q1:Attributes>" +
    xmlEntityColumns +"</q1:Attributes>" +"</columnSet>" +"</Retrieve></soap:Body></soap:Envelope>";

    //call function to create Soap Request to ms crm webservice
    xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
    xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
    xmlHttpRequest.setRequestHeader("SOAPAction", "http://schemas.microsoft.com/crm/2007/WebServices/Retrieve");
    xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
    xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
    xmlHttpRequest.send(xml);

    resultXml = xmlHttpRequest.responseXML;

    var errorCount = resultXml.selectNodes('//error').length;

    if (errorCount != 0) {
        var msg = resultXml.selectSingleNode('//description').nodeTypedValue;
        alert("Error Message : " + msg);
    }
    else {
        return resultXml;
    }
}

I have used this function to populate the contract ID text box when a contract record is selected in another dropdown.  So on an on-change event, I have the following script that calls the RetreiveEntityById.

// Only make changes to this function; you may add this function to Form Onload Event,
// Field OnChange events etc.
function GetContractId() 
{

    var EntityName, EntityId, ContractEntityId, ContractEntityName, SerialNumber, ContractId, AccountEmailAddress, LookupFieldObject, LookupContractObject;
    var PrimaryContractLookupId, PrimaryContractLookupName, PrimaryContractLookupType;
    var resultXml;

    
    LookupFieldObject = Xrm.Page.data.entity.attributes.get('new_supportid');
    

    // If lookup field has value then the code will only run
    if (LookupFieldObject.getValue() != null) 
    {

        //Fetch and place Entity Id (GUID) and Name (String) form lookup field into local variables
        EntityId = LookupFieldObject.getValue()[0].id;
        EntityName = LookupFieldObject.getValue()[0].entityType;

                 resultXml = RetrieveEntityById(EntityName, EntityId, 'contractnumber,contractid');
        // In retrieved XML document check if it has accountnumber attribute
        if (resultXml != null && resultXml.selectSingleNode('//q1:contractnumber') != null) 
        {

            // If XML document has account number attribute then assign to local variable AccountNumber
            ContractId = resultXml.selectSingleNode('//q1:contractnumber').nodeTypedValue;

            //Display Account Number Value in a Message Box
            alert("Contract ID :" + ContractId);

            //If required then use the below code line to set value in field on form
            Xrm.Page.data.entity.attributes.get('new_contractid').setValue(ContractId);
        }


        
    }
}

ANY HELP with the above is Highly Appreciated. Thank you