ASP.NET Application hosted on IIS7 that is ignoring custom errors and falls back to IIS errors

Question

I have a C# web forms ASP.NET 4.0 web application that uses Routing for URLs for some reason custom errors defined in the system.web section of my web.config is entirely ign

Answer 1

Instead of using:

Response.TrySkipIisCustomErrors = true;

Use this in Web.config:

<httpErrors errorMode="Custom" existingResponse="Replace">

Answer 2

You can pass through IIS7 default error messages in two ways One is to set response.TrySkipIisCustomErrors = true

response.TrySkipIisCustomErrors = true;
response.Status = response.Status;

For some reason, TrySkipIisCustomErrors is not honoured if you don't set response.Status.

The other is to set existingResponse to "PassThrough" in web.config

<configuration>
  <system.webServer>
    <httpErrors existingResponse="PassThrough" />
  </system.webServer>
</configuration>

But this will ignore all set IIS custom error pages.

Answer 3

To disable the IIS error messages you have to set

  Response.TrySkipIisCustomErrors = true;

in your error page. After that, your Error messages should show without problem.