Media browser from the CKeditor plugin loads blank with error

i've updated to the latest dev (7.x-2.0-alpha3+100-dev) and the media browser modal opened from the CKeditor button loads blak with the following error in the Firefox console:
"NetworkError: 500 Internal Server Error - http://drupal.ttservers.it/media/browser?render=media-popup&types=&activ..."
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TypeError: this.contentWindow.Drupal is undefined
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The javascript file that seems to throw the error is media/js/media.popups.js at line 98 (if (this.contentWindow.Drupal.media == undefined) return;")

Drupal.media.popups.mediaBrowser.mediaBrowserOnLoad = function (e) {
  var options = e.data;
  if (this.contentWindow.Drupal.media == undefined) return;

  if (this.contentWindow.Drupal.media.browser.selectedMedia.length > 0) {
    var ok = (Drupal && Drupal.t) ? Drupal.t('OK') : 'OK';
    var ok_func = $(this).dialog('option', 'buttons')[ok];
    ok_func.call(this);
    return;
  }
};

Any advice?

Thanks
Oto Tortorella