覆盖用户表单Sonata UserBundle

Hello I tried to follow the explanation given here:

How to remove fields from the admin user create page of Sonata User Bundle?

To add / remove lines to the Sonata Userbundle registration form but the problem is that I find myself for this error:

Here are the few lines of code that I put: in src/Application/Sonata/userBundle/Admin/UserAdmin.php

use Sonata\UserBundle\Admin\Model\UserAdmin as BaseUserAdmin;
use Sonata\AdminBundle\Form\FormMapper;
class UserAdmin extends BaseUserAdmin {
    protected function configureFormFields( FormMapper $formMapper ) {
        parent::configureFormFields($formMapper);
        $formMapper
            ->remove('facebookUid');
    }
}

In app/config/config.php :

sonata_user:
    security_acl: true
    manager_type: orm
    admin:                  # Admin Classes
            user:
                class:          Application\Sonata\UserBundle\Admin\UserAdmin
                controller:     SonataAdminBundle:CRUD

Can someone tell me why? Thank you

You have forgotten to declare the namespace of your UserAdmin class. It has to be the very first line of code, and will be like that in your case:

<?php
namespace UserBundle\Admin;

use Sonata\UserBundle\Admin\Model\UserAdmin as BaseUserAdmin;
use Sonata\AdminBundle\Form\FormMapper;

class UserAdmin extends BaseUserAdmin {