Update config.php

application/config/config.php

@@ -370,7 +370,7 @@ $config['encryption_key'] = '';
 $config['sess_driver'] = 'files';
 $config['sess_cookie_name'] = 'ci_session';
 $config['sess_expiration'] = 7200;
-$config['sess_save_path'] = NULL;
+$config['sess_save_path'] = sys_get_temp_dir();
 $config['sess_match_ip'] = FALSE;
 $config['sess_time_to_update'] = 300;
 $config['sess_regenerate_destroy'] = FALSE;