Backend not working

Hi. I appologize for my bad english. I have multi module (frontend, backend). somesite.cz/web - this is a frontend, works fine somesite.cz/web/administrace - this should be a backend, but not working. Im getting this error:

Web\Frontend\Controllers\IndexController handler class cannot be loaded

in services.php I have this router:

$di->set('router', function () {

$router = new \Phalcon\Mvc\Router();
$router->setDefaultModule("frontend");
$router->setDefaultNamespace('Web\Frontend\Controllers');
$router->add("/administrace", array(
            'module' => 'backend'
        ));
        $router->add('/administrace/:controller', array(
            'module' => 'backend',
            'controller' => 1,
            'action' => 'index',
        ));

        $router->add('/administrace/:controller/:action', array(
            'module' => 'backend',
            'controller' => 1,
            'action' => 2,
        ));
        $router->add(
            "/administrace/:controller/:action/:params",
            array(
            'module' => 'backend',
                "controller" => 1,
                "action"     => 2,
                "params"     => 3,
            )
        );
return $router;

});

I dont know what Im doing wrong. Please help me.