Class CI_Env not found

[Kissema]

I'm using CodeIgnitor 3, I made all configuration in the tutorial but i get this error:

` An uncaught Exception was encountered Type: Error

Message: Class 'CI_Env' not found

Filename: C:\xampp\htdocs\planils_back\system\core\Common.php

Line Number: 196

Backtrace:

File: C:\xampp\htdocs\planils_back\index.php Line: 315 Function: require_once `

[igf-cjm]

See at sys/core/Common.php add CI_ prefix to all classes on APPPATH. Why?