title: 500 Internal Server Error with W3C validator
body: <p>Our <a href="http://www.itsolutions.vn/" rel="nofollow" title="thiet ke web">website</a> is rendered OK. But when it is validated by W3C validatior (http://validator.w3.org/check?uri=http://itsolutions.vn), there is an error (500 Internal Server Error) but I don't know why.
  This causes search engines cannot index our pages.</p>
  
  <p>Could you please help me find out what is the problem?</p>