Ok, I have found temporary solution.
In grub i have the following line:
... linux /boot/vmlinuz-2.6.38-9-generic-pae root=UUID=b0da63e6-8a8d-4671-bb75-cd25c00f6585 ro vga=792 quiet splash nomodeset video=uvesafb:mode_option=1440x900-24,mtrr=3,scroll=ywrap vt.handoff=7 ....
If I change it to:
linux /boot/vmlinuz-2.6.38-9-generic-pae root=UUID=b0da63e6-8a8d-4671-bb75-cd25c00f6585 ro vga=792
the brightness control works. One boot ago I reinstalled nvidia-current. I will try to reboot and check if it still works.
Ok, I have found temporary solution.
In grub i have the following line:
... 2.6.38- 9-generic- pae root=UUID= b0da63e6- 8a8d-4671- bb75-cd25c00f65 85 ro vga=792 quiet splash nomodeset video=uvesafb: mode_option= 1440x900- 24,mtrr= 3,scroll= ywrap vt.handoff=7
linux /boot/vmlinuz-
....
If I change it to:
linux /boot/vmlinuz- 2.6.38- 9-generic- pae root=UUID= b0da63e6- 8a8d-4671- bb75-cd25c00f65 85 ro vga=792
the brightness control works. One boot ago I reinstalled nvidia-current. I will try to reboot and check if it still works.