its wrong method to create admin panel. follow below setup to setup admin.
1) go to core.php and uncomment following code
//Configure::write('Routing.prefixes', array('admin'));
2) now if you want to create login form for admin go to ur users controller and create one method which name start with 'admin_' for example admin_index
3) now open your routes.php and write following code
Router::connect('/admin', array('controller' => 'users', 'action' => 'index', 'admin'=>'true'));
now when you write http://www.example.com/admin it will go to users and admin_index method