Site behind VPN (but which has internet access) not showing up in reports (no replies)

Hi

I have a site which is behind a VPN and I have Piwik installed on a web server sat on the internet. While the google analytics code in the VPN site is able to send data to my Google Analytics account, the Piwik code is not sending data. Below is the code I have in my VPN web site pages. Is there something I need to do here to get it to start sending data to the foobar site?

<!-- Piwik -->
<script type="text/javascript">
  var _paq = _paq || [];
  _paq.push(['trackPageView']);
  _paq.push(['enableLinkTracking']);
  (function() {
    var u=(("https:" == document.location.protocol) ? "https" : "http") + "://foobar.com/piwik/";
    _paq.push(['setTrackerUrl', u+'piwik.php']);
    _paq.push(['setSiteId', 1]);
    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0]; g.type='text/javascript';
    g.defer=true; g.async=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s);
  })();

</script>
<noscript><p><img src="http://foobar.com/piwik/piwik.php?idsite=1" style="border:0;" alt="" /></p></noscript>
<!-- End Piwik Code -->