Setting Response status code causes unwanted error text at top of custom error page

Question

UPDATE:

To ensure that the correct status code is returned to the browser, the error.aspx has this line:

<% Response.StatusCode = 500; %>

Removing it removes the unwanted text, but I want the correct status code, so I suppose that is the new question...how!?

Setting the response status code has the same result:

HttpContext.Current.Response.StatusCode = 500;

Will update question title.

PRE-UPDATE:

Due to some legacy code/configuration, we have a slightly unusual custom error pages setup, which handles exceptions in the global.asax and uses Server.Transfer() to present the appropriate .aspx error page, like so:

public void Application_Error(object sender, EventArgs e)
{
    // abbreviated to clear out logging and some other logic that determines which error page to show

    HttpContext.Current.Response.Clear();
    HttpContext.Current.Server.ClearError();

    var context = HttpContext.Current;
    if (context != null)
    {
        var errorPage = "~/ErrorPages/error.aspx";
        context.Server.Transfer(errorPage);
    }
}

The issue is that when error.aspx is shown to a remote user an error message (and a new opening body tag...) is prepended to the page, so the first line of the page is unstyled text saying:

The page cannot be displayed because an internal server error has occurred.

Not ideal, and, though perhaps I am Googling the wrong things, it does not seem to be a problem that is well documented or frequently discussed.

Any ideas welcome. The error.aspx code is pretty generic but I am happy to post if it might help - please just comment.

Answer 1

The fix was to add this to the web.config:

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

Based on this answer:

IIS7 Overrides customErrors when setting Response.StatusCode?

And this blog post:

http://blogs.iis.net/ksingla/what-to-expect-from-iis7-custom-error-module

Answer 2

Did you tried to End the request?

HttpContext.Current.Response.End()

MSDN Response.End(): Sends all currently buffered output to the client, stops execution of the page, and raises the EndRequest event.