Why am I logged out after a short period?

Hi, I have a site developed using CodeIgniter and I recently moved everything to a new server. But I am having some problems in the new server.  After logging in with user (admin) I get redirected to login form.
PHP settings seems to be OK.
session.gc_maxlifetime = 1440
session.cache_expire = 180
session.cookie_lifetime = 0

Code:

$config['sess_expiration'] = 0;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = TRUE;

i have same situation some month ago using this config solved for me..