iframe url with Google Analytics no longer displaying

Question

We have been using this script for a while now to record our booking transactions through an iframe on our website, but it stopped working the other day, with no change to the code. The url no longer gets pushed into the iframe. I cannot work out why this has happened. Is there any reason the below could have stopped working that you can see, are there any alternatives?

 <iframe id="booking-frame" src="" width="975" height="1000"></iframe>
  <script>
  var iframeLink =  "https://www.xxxxxx.com"
  _gaq.push(function() {
    var pageTracker = _gat._getTrackerByName();
    iframeLink = pageTracker._getLinkerUrl(iframeLink);
    document.getElementById("booking-frame").src = iframeLink
  });
  </script>