title: "Mage registry key already exists" when firing events
body: <p>I'm Currently trying to hook into the "sales_order_save_after" event, but I constantly get the following error when the event is fired:</p>
  
  <pre><code>Mage registry key "_singleton/Modulename/Orderobserver" already exists
  </code></pre>
  
  <p>Now I've checked that the Orderobserver class is named correctly, and matches up with the call to the class in the xml, but the error is still occuring. The xml calling the event looks as so:</p>
  
  <pre><code>&lt;events&gt;
      &lt;sales_order_save_after&gt;
          &lt;observers&gt;
              &lt;modulename&gt;
                  &lt;type&gt;singleton&lt;/type&gt;
                  &lt;class&gt;Modulename/Orderobserver&lt;/class&gt;
                  &lt;method&gt;generateOrderFile&lt;/method&gt;
              &lt;/modulename&gt;
          &lt;/observers&gt;
      &lt;/sales_order_save_after&gt;
    &lt;/events&gt;
  </code></pre>
  
  <p>the class is named <code>Companyname_Modulename_Model_Modulename_Orderobserver</code>.</p>
  
  <p>The class file is named and located as so: <code>app/code/local/Companyname/Modulename/Model/Modulename/Orderobserver.php</code></p>
  
  <p>Interestingly, the following error is also logged  in the server logs when the error occurs:</p>
  
  <pre><code>client denied by server configuration: 
  /var/www/vhosts/path/to/subdomain/httpdocs/app/etc/local.xml 
  </code></pre>
  
  <p>Could this be a permissions issue?</p>
  
  <p>Update:</p>
  
  <p>I've looked in the Magento system Log, and the following error is also being logged:</p>
  
  <pre><code>Failed opening 'Mage/Retailpro/Model/Orderobserver.php' for inclusion (include_path='/var/www/path/to/subdomain/httpdocs/app/code/local:/var/www/path/to/subdomain/httpdocs/app/code/community:/var/www/path/to/subdomain/httpdocs/app/code/core:/var/www/path/to/subdomain/httpdocs/lib:.:')  in /var/www/path/to/subdomain/httpdocs/lib/Varien/Autoload.php on line 93
  </code></pre>