Firstly, Silverstripe is amazing. I am a novice and use Joomla but I will be moving to silverstripe as soon as I can manage it. Really great system.

MY PROBLEM
I thought debug mode might show me the file names so I can customize the admin easier

I added the following code to config.php

Director::set_environment_type("dev");

I then set it to
Director::set_environment_type("live");

Debug mode was not what I expected. I am a novice and it is generating an error or stuck in debug mode. I cannot be sure. I have removed the code from config.php but it is still showing the error.

I would appreciate it if someone could tell me how to get rid of debug mode/this error

*********************************************************************************
[Notice] Undefined variable: _SESSION
GET /demo/admin

Line 120 in C:\xampp\htdocs\demo\sapphire\core\control\Director.php
***********************************************************************************

Thank you.