CodeIgniter(2.1.4) Sessions is not working

CodeIgniter(2.1.4) Sessions is not working

i have a problem with CI sessions. I initialized my session library:
$autoload['libraries'] = array('database', 'session') (In
config/autoload.php).
This is my code:
cycle
$this->load->library('image_moo');
// Upload image and return unique name
$data = array(
'image' => $image,
);
$this->db->insert('category_images', $data);
if (!$this->session->userdata('uploadImages'))
{
$this->session->set_userdata('uploadImages', $this->db->insert_id());
}
else
{
$session = $this->session->userdata('uploadImages');
$sessionData = $session.'|'.$this->db->insert_id();
$this->session->set_userdata("uploadImages", $sessionData);
}
echo $this->session->userdata('uploadImages'); // return 256; corect
result - 255|256
end of cycle
This is script for image upload with jQuery File Upload(blueimp) and i
need set ids of inserted in database images to session. Can anyone help.
Thank you!