title: Symfony2 FOSUserBundle Invalid mapping file on random requests
body: <p>While deploying my <code>Symfony2</code> application to a shared webhosting platform, I noticed that on random requests, the webapplication returns a status code 500. 
  When looking in the logs, the application complains about an invalid mapping file:</p>
  
  <blockquote>
    <p><em>request.CRITICAL: Exception thrown when handling an exception (Doctrine\Common\Persistence\Mapping\MappingException: Invalid mapping file 'FOS.UserBundle.Model.User.orm.xml' for class 'FOS\UserBundle\Model\User'.</em></p>
  </blockquote>
  
  <p>I can't seem to fix this problem, it doesn't happen on each request.</p>