can't log out of facebook from App

Question

I'm trying to logout of facebook from my App using the following code below, but i'm still logged in (and my alert does not execute)

also note, this is an external App, using the facebook API.

any ideas?

FB_RequireFeatures(
  ["Api"],
  function(){

   FB.Facebook.init(api_key, channel_path);
   var api = FB.Facebook.apiClient;
   FB.Connect.logout(function(){alert("logged out!");})

  }
 );