"Unable to locate the specified class: Session.php"...

It is not clear to me exactly what problem you are having.

The loader class will find Session.php even though it is in a subfolder.

You can use

PHP Code:

var_dump($this->session); 


any place you want to check that the session library is loaded. If not loaded you will get a PHP error.

If sessions are not functioning properly it might be a config settings problem. What setting do you have for sessions and cookies?