Keyboard lighting keys are not working

Hi,

My MacBook Pro backlit keyboard recently stopped working. Even though the "Illuminate keyboard in low light condition" option is checked in the system preferences, it is not working. When I press the appropriate keys (F8, F9 and F10) all I get is the usual keyboard lighting on screen indicator, but with a "stop" sign at the bottom (see http://jext.free.fr/keyboard.png).

The sensors seem to be working since in low light conditions, the display dims. Also, I installed the tool called "Lab Tick" that lets you change the keyboard lighting brightness and it works perfectly so the keyboard itself seems fine.

I tried the following to solve this issue:
- Uncheck/check the "Illuminate keyboard..." option ;
- Reset the PRAM ;
- Reset the PMU ;
- Erase and re-generate the BezelServices preferences in both ~/Library and /Library.

I would be really grateful if any of you had further ideas on how to solve this issue.

Thanks!