Can't extend a class in a CLI application

Hi, title is clear. I can't extend a class in my CLI application. All the following classes are in the lib folder :

class FraudTask extends \Phalcon\CLI\Task {

    public function mainAction() {

        $liveFraud = new LiveFraud();
        $liveFraud->execute();

        //$liveMobileFraud = new LiveMobileFraud();
        //$liveMobileFraud->execute();
    }
}

class LiveFraud extends Fraud {
}

abstract class Fraud  {
}

In my config file :

$loader->registerDirs(

array(

    APPLICATION_PATH . '/tasks',
    APPLICATION_PATH . '/models',
    APPLICATION_PATH . '/lib',
));

$loader->register();

When I execute : php cli.php fraud

Fatal error: Class 'Fraud' not found in /Library/WebServer/Documents/tuangocli/app/lib/LiveFraud.php on line 30

I don't understand why the class is not found.