Could not load type "formextra_recaptcha"

[sunviwo]

I get this error and I don't know why. Any help ?

[stof]

have you enabled the recaptcha in the bundle, by configuring it ?

[sunviwo]

Yes, I followed the documentation and here is what I put in my config.yml
simple_things_form_extra:
recaptcha:
public_key: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
private_key: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx