Unibody MBP with 10.6.2 forgets to auto-dim its display after about a day

[Pax]

After about a day of use my Unibody MBP 13" running 10.6.2 forgets how to auto-dim its display. The "automatically adjust brightness" checkbox is still checked, but the display doesn't change brightness even if I put my thumb over the sensor. Checking & unchecking the box makes no difference. Trashing ~ System Preferences .plist makes no difference.

If I switch to another user that user still has auto-dimming working OK. If I log out and in again auto-dim works again for a day or two. So it seems like software and not hardware. I've also reset the SMC, no difference.

Does anyone
- have the same problem?
- know what bit of software handles auto-dim:- is there a process I can quit and relaunch?
- have any other useful suggestions eg about .plist trashing?

Thanks

 

[Pax]

The keyboard backlight auto-dim still works, it comes on and brightens and dims as I expect. Even though at the moment the LCD has forgotten to do so.