Reading your error it seems that your application isn't able to find APPPATH and PKGPATH. They should be defined in the /public/index.php file.
This is my configuration:
/**
* Website document root
*/
define('DOCROOT', __DIR__.DIRECTORY_SEPARATOR);
/**
* Path to the application directory.
*/
define('APPPATH', realpath(__DIR__.'/../fuel/app/').DIRECTORY_SEPARATOR);
/**
* Path to the default packages directory.
*/
define('PKGPATH', realpath(__DIR__.'/../fuel/packages/').DIRECTORY_SEPARATOR);