X11 telling me "Newer software allready exists on this computer"

I can’t install Ardour2.1 for Mac OS X (i run 10.4.11 on Intel), because it tells me to install X11 before running the app.
I downloaded X11 from apple.com, but X11 installation tells me “You cannot install X11 on this volume. Newer Software already exists on your computer”.

What is this “Newer Software”? I’m stuck =/

Do not download X11 from the Apple website, it provides an outdated version. Instead, install X11 from your OS X install disk and after update it with software update

That was a great help. Thank you.