It is possible that the failure warning relay is going bad. Especially if you get a warning when you first start the car and no lights have been turned on yet and you haven't put your foot on the brake. (If someone can think of a monitored bulb that comes on under that condition, please tell me.)

The problem is that it is an expensive relay to swap-out, and it would be a rather complex one to get into and resolder all the solder paths.