Codeigniter在本地mamp上升级2.0.2到3.1.10会话问题

Question

I'm updating my Codeigniter. I've deleted de system folder and replaced it with the new one. I've followed the Upgrading from 2.2.x to 3.0.x instructions. These are my new settings for the session:

$config['sess_driver']      = 'files';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration']  = 0;
$config['sess_save_path']   = APPPATH.'/sessions';
$config['sess_match_ip']    = FALSE;

$config['sess_time_to_update']     = 300;
$config['sess_regenerate_destroy'] = FALSE;

$config['cookie_domain']   = '';
$config['cookie_path']     = '/';
$config['cookie_secure'    = FALSE;

I use:

  $newdata = array(
          'username'  => $member->email,
          'email'     => $member->member_id,
          'logged_in' => TRUE
  );

  $this->session->set_userdata($newdata);

I can print user, email after the set_userdata, but when I redirect to the default page in my admin, I get

$_SESSION empty

(except for the __ci_last_regenerate )

The folder is "OK"(I can see the new session).

I'm using MAMP PRO 5.3 with on port 8890 for ssl. I've tried database driver with same results.