Please follow the below steps:
1) Go to system/libraries/Session/Session.php
2) Comment session_start() by adding //.
3) Go down to line around 312-315 where it says Security is king, and comment out the following lines:
ini_set('session.use_trans_sid', 0);
ini_set('session.use_strict_mode', 1);
ini_set('session.use_cookies', 1);
ini_set('session.use_only_cookies', 1);
ini_set('session.hash_function', 1);
ini_set('session.hash_bits_per_character', 4);
4) Then go to your main index.php ( the root index.php )
5) Add session_start() at the top once.
It works for me.