title: Service Unavailable 503 when trying to update to ASP.NET 4
body: <p>I am trying to update my web application from 3.5 to 4.0. I've changed to ASP.NET 4.0 Integrated application pool and removed from web.config all the unnecessary tags.</p>
  
  <p>When I try now to access my site it says:</p>
  
  <blockquote>
  <pre><code>Service Unavailable
  </code></pre>
    
    <p>HTTP Error 503. The service is unavailable.</p>
  </blockquote>
  
  <p>When I look in EventViewer for details I see:</p>
  
  <pre><code>Application pool 'ASP.NET 4.0 (Integrated)' is being automatically disabled due to a series of failures in the process(es) serving that application pool.
  </code></pre>
  
  <p>For one of the previous events I notice for instance:</p>
  
  <pre><code>A process serving application pool 'ASP.NET 4.0 (Integrated)' terminated unexpectedly. The process id was '4040'. The process exit code was '0xfffffffe'.
  </code></pre>
  
  <p>I am not able to find other details for this issue which gets me desperate..Can you please give me any clue?</p>