Error 404 - Not Found -The requested document was not found on this server.

[auri501]

Buenos días a todos,
Estamos intentando controlar el error 404 mediante un archivo personalizado, y tras incluir "ErrorDocument 404 /error404.html" en /etc/apache2/errors.conf por ssh y subir dicho archivo a la raiz del sitio, nos aparece el siguiente error:
"Error 404 - Not Found -The requested document was not found on this server." y en el código fuente lo siguiente:
- Unfortunately, Microsoft has added a clever new
- "feature" to Internet Explorer. If the text of
- an error's message is "too small", specifically
- less than 512 bytes, Internet Explorer returns
- its own error message. You can turn that off,
- but it's pretty tricky to find switch called
- "smart error messages". That means, of course,
- that short error messages are censored by default.
- IIS always returns error messages that are long
- enough to make Internet Explorer happy. The
- workaround is pretty simple: pad the error
- message with a big comment like this to push it
- over the five hundred and twelve bytes minimum.
- Of course, that's exactly what you're reading
- right now.

Nuestro archivo error404.html pesa más de 512 bytes y no sabemos porque no lo reconoce. ¿Alguien tiene idea porque puede dar este error?

Muchas Gracias!!