Whenever I browse to a non-existent file, I get the standard apache 404 message instead of my own. Plus, interestingly, a message saying it failed with the custom 404. The exact message:
The requested URL /123 was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
I am not using structured permalinks, if that has any relevance (a restriction of my host).
The site is http://ijamming.net if you want to see for yourselves.