404 error not working properly

What happens on the main site?

redirects to the home page

Did you re-save permalinks on the main site?

permalinks are set to:

/%day%/%monthnum%/%year%/%postname%/

at the moment

Right, just click the SAVE permalink button on that page to re-save them ?? It flushes the re-write rules, you see, and regenerates.

okay, just saved them permalinks, and tried a non existing page. Still redirecting back to home page ??