ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in codeigniter
Open the config.php and add ob_start(); it will help to delay the sending of the HTTP header
Look at the example below
<?phpdefined('BASEPATH') OR exit('No direct script access allowed');ob_start();
For me the error occured because i accidentally added some empty lines after php closing bracket ?> in a helper class i loaded before loading the session library.