IIS6 - Why won't my Custom error page display?

I have a custom error page that should display for HTTP 404 errors. It does not and I am having difficulty figuring ou开发者_StackOverflowt why.

My web.config is set

<customErrors mode="On" />

Fiddler shows a 401.2, followed by a 404 for a single POST. Both errors should be custom. The 401.2 is working because I see it in fiddler. The 404 happens immediately after so all I see in the browser is the generic 404 error. I should see my custom 404 page.

Why won't my custom HTTP 404 page showup?

What's the URL you are testing with? If it's not a file type handled by ASP.NET (e.g. /foo/bar.txt) then you won't see the ASP.NET defined 404 handler.

-Oisin

If you're looking for what the 404.x codes mean here's this

HTTP 404.x-File or Directory Not Found

• None - File or directory not found.
• 1 - Web site not accessible on the requested port.
• 2 - Web service extension lockdown policy prevents this request.
• 3 - MIME map policy prevents this request.

Seems to be an IIS specific code, not sure if IIS sends these details with the response