Library not loading in Google App Engine

Hard to know without having any errors present. My best guess would be the way you are pointing to the file is wrong. I have had this issue a few times. Works perfectly on a local machine and then doesn't work on the remote server. App engine I haven't tried yet as they are still in beta for php.
Have you got error reporting turned on in your index.php file?

PHP Code:

       case 'development':
        error_reporting(E_ALL);
    break; 


Regards
woody1990