title: IIS 7, HttpHandler and HTTP Error 500.21
body: <p>On IIS 7, I'm trying to use custom HttpHandler for my ASP.NET web application. I use pipeline mode "classic", .NET version is 4.0.30319, my web.config configuration for the handler is: </p>
  
  <pre><code>&lt;system.webServer&gt;
  &lt;handlers&gt;
      &lt;add name="MyHandler" path="*.myExtension" verb="*" type="Company.App.UI.Controls.MyHandler, Company.App.UI" resourceType="Unspecified" /&gt;
  &lt;/handlers&gt;
  &lt;/system.webServer&gt; 
  </code></pre>
  
  <p>When I invoke this handler, I get this error:</p>
  
  <pre><code>HTTP Error 500.21 - Internal Server Error
  Handler "MyHandler" has a bad module "ManagedPipelineHandler" in its module list
  </code></pre>
  
  <p>I did a google search, the most of people fix this issue by re-registering ASP.NET by aspnet_regiis.exe /i command, but this is <strong>not</strong> working for me (the command finishes, I restart the IIS, but same error). I tried it on two different servers, but got the same result. </p>
  
  <p>What else should I try? Thank you</p>