Problems with reCAPTCHA library from the wiki

[eluser]sorenchr[/eluser]
Hi, I'm using the reCAPTCHA library from the wiki:

http://codeigniter.com/wiki/ReCAPTCHA/

My code looks like this in my model:

Code:

$this->load->library('recaptcha');
$this->lang->load('recaptcha');
$response = $this->recaptcha->check_answer($this->input->ip_address(),$this->input->post('recaptcha_challenge_field'),$this->input->post('recaptcha_response_field'));
echo $response;

But $response is empty when I use it! I've got the library file in my application/libraries and the config file in application/config. I can see the POST-data from the recaptcha_challenge_field and recaptcha_response_field, so they are sending data.