That's a system page, you don't edit it, but you can override it and use a custom page in its place, by adding similarly named page to the theme of your site.

This tutorial covers it in detail

http://www.codeblog.ch/2010/01/concrete5-custom-404-page/...

Thank you very much for posting..

I know it's a system page, and I have overridden it, so I'm not editing the system page (in the concrete dir).

But even after I've overridden it, it still doesn't show the edit bar on the top of the page, when I'm logged in, so that is my problem..

Regards
Kim Andersen

You won't be able to edit it from the interface.

If you want to append some alternative/addtional logic to the page not found page, that is being displayed using your custom themes page, then you need to duplicate the single page that is used.

Create a copy of /concrete/single_pages/page_not_found.php and place it here /single_pages/page_not_found.php.

This page will now be used and represent all the content that is being shown in the $innerContent variable. If you want to edit it, edit it in the page you've just created with a text editor.

Hope that helps.

Okay thanks..

But what if I want the header menu, how would I go about that ?

Thank you very much for all your help..