 <p>First of all, does the page load when you just try to render it or does that crash? </p> <p>If that works, the next thing to check is that if you look in the web.config, there is a url that is specified the validation check. See what you have listed. This should be the default. </p> <pre class="lang-xml prettyprint-override"><code>&lt;setting name="HtmlEditor.ValidatorServiceUrl" value="http://validator.w3.org/check" /&gt; </code></pre> <p>If it's not set to that value, put that in and try again. If you are able to get to that page, see if it validates manually. If its able to check manually and return a successful result, then I'd suggest putting in a ticket to Sitecore support. </p>