$autoload['libraries'] = array('session'); error

Your session configuration shows that you are using the *files* driver, but you have not set the *session_save_path* to a valid folder for the session driver to use.

https://www.codeigniter.com/user_guide/l...references
https://www.codeigniter.com/user_guide/l...les-driver

If you think you have configured it to use the database driver, the error message quite explicitly tells yoiu it is trying to use the files driver.