Internal Server Error in crm 2013

Hi,

when i get lookup attribute value Internal server error occurred. Please tell me how to resolve my issue

here is my script 

function GetEmail() {
var EntitySchemaname="new_datacentreSet";// may be new_buyerSet ?
var Relationshipname="new_new_datacentre_new_dealer_DataCentre";

var Buyerlookup=Array();
Buyerlookup=Xrm.Page.getAttribute("new_DataCentre").getValue();
alert(Buyerlookup[0].id);
if (Buyerlookup == null || Buyerlookup == undefined)
{
alert("sorry");
}
else
{
serverUrl = Xrm.Page.context.getClientUrl();
var req = new XMLHttpRequest();
req.open('GET', encodeURI(serverUrl + "/XRMServices/2011/OrganizationData.svc/"+EntitySchemaname+"(guid'" + Buyerlookup[0].id + "')?$select=new_Website,Relationshipname"), true);
 req.setRequestHeader('Accept', 'application/json');
 req.setRequestHeader('Content-Type', 'application/json; charset=utf-8');
 req.onreadystatechange = function () {
 if (this.readyState == 4) {
 req.onreadystatechange = null;
 if (this.status == 200)
 { var result = JSON.parse(req.responseText).d;
 var EMailAddress1 = result.new_Website; // change this field with new_email schema name
 alert(EMailAddress1); }
 else { alert(this.statusText); } } };
 req.send();
}
}