Custom 403 not displaying

I created a custom 403 forbidden page, but it’s not displaying. The default forbidden page displays an error message: “Additionally, a 400 Bad Request error was encountered while trying to use an ErrorDocument to handle the request.”

I tried using standard HTML in this file after finding that calls to the header, sidebar, and footer didn’t work. It still doesn’t work though, so I’m thinking that the error message doesn’t have anything to do with calling those other pages.

Could anyone help me? Try typing this URL to see what happens:
http://suefeng.com/wp-config.php