Ok, so I'm currently testing an add-on I've written (which works perfectly in PHP 5.3) in PHP 5.4 and I am getting a Fatal error. Specifically: Fatal error: Class 'Facebook' not found in C:\xampp\htdocs\library\AddOn\ControllerPublic\AddOn.php on line 508. The add-on uses a Facebook API. Here's some relevant code: PHP: include_once 'library/AddOn/facebook/src/facebook.php'; Then other relevant code (beginning on the aforementioned line 508): PHP: $facebook = new Facebook(array( 'appId'=> $fbapp_id, 'secret'=> $fbapp_secret,));return $facebook; facebook.php (this is the Facebook SDK, not my code) contains: PHP: class Facebook extends BaseFacebook Any ideas on a solution? Again, it works perfectly on 5.3... just a 5.4 specific bug (again).