hi again, thanks for your answers.
i removed all security from my domain, so that brontocorp.heliohost.org returns a simple index.html with this text: "this site is just this page".
However, i'm still having the internal server error in the subdomain... On the other hand, if i access cbvusb.brontocorp.heliohost.org/index.html, that page actually loads properly, wich only have the text "ejemplo".
Finally, there's nothing in the Cpanel's error log :S so i'm really confused, i think i have to configure some routing but i don't know how can i achieve that.
Thanks for your attention.