XrmToolkit Retrieve Related Entity's Lookup Field

I have a custom entity, which is related to a custom "property" entity that has a contact lookup on it. I want to retrieve that contact. In the code below, I am supplying the guid of the "property" entity, along with the "nna_ownercontactid" column. I get "success" but it reports "undefined" for that column, and every other column (including even a "name" column.) I've tried it with and without the "nna" prefix for this and other columns as well.

What am I missing? As a point of reference, I built this using the Retrieve function from Sumedha Obeysekera's blog below. The Retrieve function worked fine, but not mine. Thanks for your help!

function RetrievePropertyContact(prop2) {
    var re;
    XrmServiceToolkit.Rest.Retrieve(
              "{" + prop2 + "}",
              "nna_propertySet",
              null, null,
              function (result) {
                  re = result;
                  alert("success");
                 alert(re.nna_ownercontactid);
                 },
              function (error) {
                  alert("failed");
              },
              false
          );
    //debugger;
alert(re.nna_ownercontactid);
 }

sumedha8.blogspot.co.uk/.../rest-functions-from-xrmservicetoolkit.html

function Retrieve() {
    var re;
    XrmServiceToolkit.Rest.Retrieve(
              "{EE81D2A9-E28E-E311-96DF-D89D6765B238}",
              "AccountSet",
              null, null,
              function (result) {
                  re = result;
                  alert("success");
              },
              function (error) {
                  alert("failed");
              },
              false
          );
    //debugger;
    alert(re.Name);
    alert(re.AccountId);
}