codeigniter version upgrade

I need assistance with resolving errors that appeared after upgrading CodeIgniter from version 3.1.10 to 3.1.13. Specifically, there are undefined variable errors for some variables in the controller file and an error in the index.php file require_once. Additionally, there is an error in an array with the message "Undefined offset: 1" and a backtrace. I would appreciate any help in resolving these issues.

Please post your code here, with the detailed error message that you had, so the others can help.