parameters.yml

parameters:
    database_host: 127.0.0.1
    database_port: null
    database_name: database
    database_user: root
    database_password: root
    mailer_transport: smtp
    mailer_host: 127.0.0.1
    mailer_user: null
    mailer_password: null
    secret: b312a59f402658b3e49535bacb479b8ae704eba7

register_content.html.twig

{% trans_default_domain 'FOSUserBundle' %}

{{ form_start(form, {'method': 'post', 'action': path('fos_user_registration_register'), 'attr': {'class': 'fos_user_registration_register'}}) }}
    {{ form_widget(form) }}
    <div>
        <input type="submit" value="{{ 'registration.submit'|trans }}" />
    </div>
{{ form_end(form) }}

security.yml

security:
    encoders:
        FOS\UserBundle\Model\UserInterface: bcrypt

    role_hierarchy:
        ROLE_ADMIN:       ROLE_USER
        ROLE_SUPER_ADMIN: ROLE_ADMIN

    providers:
        fos_userbundle:
            id: fos_user.user_provider.username

    firewalls:
        main:
            pattern: ^/
            form_login:
                provider: fos_userbundle
                csrf_token_generator: security.csrf.token_manager
                # if you are using Symfony < 2.8, use the following config instead:
                # csrf_provider: form.csrf_provider

            logout:       true
            anonymous:    true

    access_control:
        - { path: ^/login$, role: IS_AUTHENTICATED_ANONYMOUSLY }
        - { path: ^/register, role: IS_AUTHENTICATED_ANONYMOUSLY }
        - { path: ^/resetting, role: IS_AUTHENTICATED_ANONYMOUSLY }
        - { path: ^/admin/, role: ROLE_ADMIN }

My form and error