DMS Backlight Issue

Hi,
Just wondering if anyone has experienced a probelm with DMS backlights not working? We have a client who had requested that the backlights be turned on permanantly. I programmed the keypads so that there is no timeout on the backlight while also explaining that the screen would fade over time, which inevitably has happened. This seemed to work fine at the start but recently the client has complained that the backlight is not working on some of the units. I fixed this the first time by reloading all the keypads into the system and rebooting the NXI, but now it has happened again! Any ideas whats happening and how i could fix this permanantly?

Cheers,
Shane