MSCRM 2011 Javascript not working

Hi, the following code are the javascript that i apply in my crm case form.

function AssignToMe() {
 var context;
 var serverUrl;
 var UserID;
 var ODataPath;
 context = Xrm.Page.context;
 serverUrl = context.getServerUrl();
 UserID = context.getUserId();
 ODataPath = serverUrl + "/XRMServices/2011/OrganizationData.svc";
 var retrieveUserReq = new XMLHttpRequest();
 retrieveUserReq.open("GET", ODataPath + "/SystemUserSet(guid'" + UserID + "')", true);
 retrieveUserReq.setRequestHeader("Accept", "application/json");
 retrieveUserReq.setRequestHeader("Content-Type", "application/json; charset=utf-8");
 retrieveUserReq.onreadystatechange = function () {
 retrieveUserReqCallBack(this,UserID);
 };
 retrieveUserReq.send();

}

function retrieveUserReqCallBack(retrieveUserReq,UserID) {
var CurrentUser = Xrm.Page.getAttribute('ownerid').getValue();
var CurrentUserId = CurrentUser[0].id;
if (retrieveUserReq.readyState == 4 /* complete */) {
if (retrieveUserReq.status == 200) {
 var retrievedUser = this.parent.JSON.parse(retrieveUserReq.responseText).d;
 if ((retrievedUser.FullName != null) && (CurrentUserId != UserID))
  {

var setUservalue = new Array();
 setUservalue[0] = new Object();
 setUservalue[0].id = Xrm.Page.context.getUserId();
 setUservalue[0].entityType = 'systemuser';
 setUservalue[0].name = retrievedUser.FullName;

Xrm.Page.getAttribute("ownerid").setValue(setUservalue)
Xrm.Page.data.entity.save();
 }
 }
}
}

I would like to ask, why the javascript not working when i access  URLhttp://IP/DEV/. but its working if i access URL http://localhost/DEV/. both are same eviroment.

Thank you