Session doesn't work after update from 2.2.1 to 3

Hello, before few days I update my CI using this tutorial and now even though that I've choose driver to be "files", CI tries to save my session in the db.
I have encryption key in the config and this is my session config

PHP Code:

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300; 


This is my code

PHP Code:

$session = array(
                'email' => $user,
                'user_id' => $id                
            );
            $this->session->set_userdata($session); 


and this is the result http://grab.by/F0mk

I tried to use $_SESSION, but it gives me the same error.

On another project I put fresh 3.0 version and I used the same code for new session and everything is okay... Any ideas what to do?