Bug is easy to spot if you enable notices (or simply set the wp debug to true).
Two notice errors annoyingly appear:
NOTICE: wp-content/plugins/facebook-feed-grabber/facebook.php:588 - Trying to get property of non-object
NOTICE: wp-content/plugins/facebook-feed-grabber/facebook.php:589 - Trying to get property of non-object
You'are using object reference where it is an array. The more strange is that you used array reference one line earlier :D
Please fix. This should be easy one.