Genemu reCaptcha没有在Symfony2 Twig中显示

I'm using the GenemuFormBundle for the reCATPCHA usage in my form.

I followed the instructions and searched for a solution, but i couldn't find one that is working for me. The Captcha just doesn't shows up!

My config.yml

genemu_form:
    recaptcha:
        public_key:  `12345`
        private_key: `54321`

I also tried it without the `, but the same result.

My FormBuilder, this form stands by itself and isn't mapped with a entity.

$form = $this->createFormBuilder()
            #....
            ->add('captcha', 'genemu_recaptcha')
            ->getForm();

And mit support.twig.html file where the captcha should be shown

{% block stylesheets %}
    {{ parent() }}
    {{ form_stylesheet(form) }}
{% endblock %}

{% block javascripts %}
    {{ parent() }}
    {{ form_javascript(form) }}
{% endblock %}

{% block body %}

    {{ form_start(form) }}

    <p>{{ form_label(form.name, 'Name *') }}
        <span class="contact_form_widget">{{ form_widget(form.name)}}</span></p>

    <p>{{ form_label(form.email, 'E-Mail Adresse *') }}
        <span class="contact_form_widget">{{ form_widget(form.email)}}</span></p>

    <p>{{ form_label(form.website, 'Website') }}
        <span class="contact_form_widget">{{ form_widget(form.website)}}</span></p>

    <p>{{ form_label(form.subject, 'Betreff *') }}
        <span class="contact_form_widget">{{ form_widget(form.subject)}}</span></p>

    <p>{{ form_label(form.message, 'Ihre Anfrage *') }}
        <span class="contact_form_widget">{{ form_widget(form.message)}}</span></p>

    {{ form_rest(form) }}

    {{ form_end(form) }}
</div>

What am i doing wrong or what am i missing?