Comment 8 for bug 566134

I am also affected by this problem.
HP Pavilion DV6 2160eh (Nvidia GeForce G105M) Ubuntu 10.10 Maverick

It used to work fine (in 9.10).

Maybe because of control keys are swapped... (https://bugs.launchpad.net/ubuntu/+source/udev/+bug/638638)

I can change brightness by set manually in CLI as root which are working fine:
   #in this case brightness applet gets the new percentage as well (better):
   acpi_fakekey 224 #bright down by 10% (exec it more times result darker)
   acpi_fakekey 225 #bright up by 10% (exec it more times result lighter)

   or

   #setting this parameter manually does not have an effect on brightness applet
   cat /proc/acpi/video/VGA1/LCD/brightness # show current values and ranges
   BRIGHT="50" #values could be: 0-100
   echo "$BRIGHT" > /proc/acpi/video/VGA1/LCD/brightness

If I set manually the brightness to 50 and I start acpi_listen, then check brightness current parameter in case of keypress
# FN+F7 (bright down key): video LCD 00000087 00000000
   - results: current=0 and LCD brightness lighting as maximum until some of the acpi events (eg. power management changes)
   - pressing more times results nothing else

# FN+F8 (bright up key): video LCD 00000086 00000000
   - results: current=10 and brightness goes to that level (10%)
   - pressing more times results: it is trying to be lighter but after releasing goes back to 10%