title: CodeIgniter: Class 'CI_Controller' not found
body: <p>I've extended CodeIgniter controller by adding MY_Controller.php in Application/Core folder. It works fine, but Now when I add following code on <code>error_404.php</code> page in <code>Application/errors</code>, I get error.</p>
  
  <p><strong>Code causing problem:</strong></p>
  
  <pre><code>&lt;?php $ci =&amp; get_instance();?&gt;
  &lt;?php $this-&gt;ci-&gt;load-&gt;view('header')?&gt;
  </code></pre>
  
  <p><strong>Error:</strong></p>
  
  <pre><code>Fatal error: Class 'CI_Controller' not found in path\to\system\core\CodeIgniter.php on line 231
  </code></pre>
  
  <p>The line 231 of the <code>system\core\CodeIgniter.php</code> is:</p>
  
  <pre><code>function &amp;get_instance()
      {
          return CI_Controller::get_instance(); 
      }
  </code></pre>
  
  <p>How can I fix this so that I can load view in the error_404.php without changing anything in system files.</p>
  
  <p>PS. I'm using latest version.</p>
  
  <p>Thanks.</p>