I am getting error while storing sessions into db in codeigniter3

After login i am getting the error: Message: ini_set(): A session is active. You cannot change the session module's ini settings at this time

$config['sess_driver'] = 'database'; #files, database
$config['sess_cookie_name'] = 'ci_sessions';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = 'ci_sessions';//its your table name, files=NULL
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;

this is my config file.