For some reason, the code being generated inside Facebook developer does not work. Actually, the problem is on the profile_id parameter which is not recognized by the likebox.php. Instead, id should be used.

<iframe src="http://www.facebook.com/plugins/likebox.php?id=**[YOUR_PAGE_ID_HERE]**&width=298&connections=10&stream=false&header=true" scrolling="no" frameborder="0" allowTransparency="true" style="border:none; overflow:hidden; width:298px; height:290px"> </iframe>

If still that doesn't work, then you can use the legacy code as below. <iframe src="http://www.facebook.com/connect/connect.php?id=**[YOUR_PAGE_ID_HERE]**&connections=10&stream=0&locale=en_US" allowtransparency="true" style="border: medium none; width: 300px; height: 240px;" scrolling="no" frameborder="0"></iframe>

I tried both and they all worked as expected.

Source: http://forum.developers.facebook.net/viewtopic.php?id=56454&p=1