Why can't I get my site to recognize a default error page for status code 404 in a WebMatrix WebPages environment?

Question

I have seen in multiple places

[here] http://www.localwisdom.com/blog/2010/08/how-to-setup-custom-404s-for-iis-and-asp-net-through-web-config/

[and from a previous question here] How can I make a custom error page in ASP.NET web-pages with WebMatrix?

how to setup the web.config file to force custom error pages for given status codes (I think the only ones I care about are "500" and "404").

I am using this as the <system.web> element in the web.config XML.

<system.web>
    <compilation debug="true" targetFramework="4.0"><assemblies><add assembly="System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /></assemblies></compilation>
    <customErrors mode="On">
        <error statusCode="500" redirect="~/Error.cshtml" />
        <error statusCode="404" redirect="~/Error404.cshtml" />
    </customErrors>
</system.web>

The custom error page for the status code, "500" serves up just fine on normal server-side errors, but for some reason, no matter what I do, I can't seem to get the custom error page for status code "404" to show up if, say, a broken link were clicked on the page. Instead, it just shows the normal "404, resource not found" default page.

I have also tried to change the order of the <error> tags (not that that should help, but as you can see, I am out of reasonable things to try, LOL).

Am I misunderstanding how this whole thing works or am I simply getting the configuration/syntax wrong in some way?

--------------------------------UPDATE----------------------------------------

Okay, so apparently, my custom 404 page works if a normal link is broken, however, I have .cs file with certain html generating methods in it.

On a single secondary page, this will be it's entire contents:

@Html.Raw(ContentGenerator.Generate("CityCouncil"))

The values for what to display on the page come from a database, are encoded as they are added to the string, and then written to the page. If the C# string contains a broken link, then the default error page does not show up. Why should this make a difference? My guess is, it's a timing issue, and that by the time C# writes the HTML to the page, the web.config file can no longer influence this link or something.

Is there any way to still achieve a default error page for these links?

Answer 1

The customErrors entry in your web.config under system.web works for urls with file extensions as we have established. but to work for extension-less urls, you need to override IIS by adding an entry to the system.webServer node in your web.config:

<system.webServer>
    <httpErrors existingResponse="Replace" errorMode="Custom">
        <remove statusCode="404" subStatusCode="-1" />
        <error statusCode="404" prefixLanguageFilePath=""
               path="/Error404.cshtml" responseMode="ExecuteURL" />
    </httpErrors>
</system.webServer>

Having done this, you also need to move any other custom error handling to the system.webServer section and remove the customErrors entry under system.web.