Comment 2 for bug 484715

ext73 can you please try to put on your panel the 'Power Manager Brightness Applet' and check if you can change the brightness using it?
Thanks

P.S.:
I just saw a new notification in my notification area that seems to be relevant.Right clicking or just clicking does nothing.When I mouse over it a message appears :
""Session active, not inhibited, screen idle. If you can see this text, your display server is broken and yoy should notify your distributor.
Please see http://blogs.gnome.org/hughsie/2009/08/17/gnome-power-manager-and-blanking-removal-of-bodges/ for more information""