web.config and 500 Internal server error

I am attempting to the get web.config file to display a more detailed message than 500 Internal server error. I added this block of code to the web.conf file and it still displays the error. Although it is prettier.

 <system.webServer>
    <httpErrors errorMode="Detailed" />
    <asp scriptErrorSentToBrowser="true"/>
  </system.webServer>
  <system.web>
    <customErrors mode="Off"/>
    <compilation debug="true"/>
  </system.web>

It is an application located in a sub-folder. Also, when I add this code it gives me the same error on the home page. If I take it out the homepage shows up again.

Thank you for your help!