Why does this code throw a Facebook API Error 191?

Question

I have the following config.php file sitting at www.sitename.com/facebook/

Answer 1

Reason for error 191:

In Facebook Application Setting, Site URL is not same as REQUEST_URI (Redirecting URL) e.g., if you specified site URL to http://www.sitename.com/facebook/ then you are not allow to redirect to http://www.namesite.com/facebook/