How to add kathmann's Auth_AD into my project?

[eluser]Unknown[/eluser]
I want to add Active Directory authentication to my project. Kathmann's Auth_AD library http://ellislab.com/forums/viewthread/234440/ looks just the job. I've downloaded the files and saved them in the correct locations. Now what?
If I try editing application/config/autoload.php with

Code:

$autoload['libraries'] = array('Auth_AD');

I get a 500 error.
If I try application/controllers/pages.php

Code:

class Pages extends CI_Controller {

public function view($page = 'home')  //this is a method.
{
  $this->load->helper('url');   // url variables.
  $this->load->library('Auth_AD');

I have the same problem.

Any pointers?

Notes: php 5.5 on IIS7. (I know, but it's a company intranet project.)

[eluser]Unknown[/eluser]
Solved!

The browser wasn't giving me any help but I thought of running the script from the Windows command line.

Code:

php index.php

This gave me the error message

Code:

An Error Was Encountered
In order to use the Session class you are required to set an encryption key in your config file.

Off to application/config/config.php and add in the key:

Code:

$config['encryption_key'] = 'myEncryptionKey';

... and the page displays in the browser.

Now to understand the rest ...