I want to track the status of facebook likes and unlikes in Analytics but am having problems.

The following code, copied from the Analytics documentation [here](http://code.google.com/intl/sv-SE/apis/analytics/docs/tracking/gaTrackingSocial.html), is not working for me. 

```
FB.Event.subscribe('edge.create', function(targetUrl) {
  _gaq.push(['_trackSocial', 'facebook', 'like', targetUrl]);

});

```

I've put that code snippet in my sites footer but the error message says: "FB not defined", checked with Firebug. Since I have a facebook-box on my site containg a like button I thought that the FB-related code would be loaded and not undefined.

The facebook-box I have is iframed. Is that why it wont work? What would I have to do to start tracking the like-button in my facebook-box in Analtycs?