there was a change this month:

https://developers.facebook.com/roadmap/#july2013

Social plugins will require an absolute URL in the 'href' parameter
Social plugins, such as the Like Box and Like Button, will require an absolute URL in the 'href' parameter.

the new codes look like this:

https://gist.github.com/DanielRuf/5983863

I have replaced the iframe on the promo page using Google Chrome Developer Tools and it worked =)

;-)