facebook-page-photo-gallery.php line 493 references 'fppg_version', I believe should be 'fppg_active_version'
Two other debug errors:
on gallery page:
Notice: Undefined property: stdClass::$name in /.../wp-content/plugins/facebook-page-photo-gallery/facebook-page-photo-gallery.php on line 164
Notice: has_cap was called with an argument that is deprecated since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /...`/wp-includes/functions.php on line 3466