Can't create thumbs using Image Manipulation class

[eluser]chitoso[/eluser]
rom what I've seen in the docs (http://ellislab.com/codeigniter/user-gui...e_lib.html):
"If only the path is specified, the new image will be placed in the destination with the same name as the original.", so I assume this code should work.

Code:

$config_image['image_library'] = 'gd';
$config_image['source_image'] = $data['full_path'];
$config_image['new_image'] = 'uploads/proyectos/thumbs/';
$config_image['create_thumb'] = TRUE;
$config_image['maintain_ratio'] = TRUE;
$config_image['width'] = 120;

$this->load->library('image_lib', $config_image);

if (!$this->image_lib->resize()) {
    $this->session->set_flashdata('message', $this->image_lib->display_errors());
}

The weird thing is that it fails silently, no errors whatsoever. Any clues?