title: In order to use the Session class you are required to set an encryption key in your config file
body: <p>I am in the process of upgrading codeigniter from 1.7.2 to 2.0.1.</p>
  
  <p>Everything seems to have gone ok except I get</p>
  
  <blockquote>
    <p>In order to use the Session class you are required to set an encryption key in your config file.</p>
  </blockquote>
  
  <p>What is the change in 2.0.0/2.0.1 that has caused this?</p>
  
  <p>What change do I need to make to fix this.</p>
  
  <p>Will making said change break anything?</p>