Check Brake System Warning

In addition to the cold start problem (see other thread), A few times over the last month I will get a dash warning on start up the Check Brake System with that non stop annoying beep. This is an independent problem to the cold start, it happens when the truck is plenty warmed up. If I shut the truck off and let the computer reset then start back up, it either goes away or I have to repeat the process a few times to get the warning to go away. One time, I drove it accross the parking lot with the warning still on to see if the brakes felt wierd or something. They felt normal. This has only happened 4-5 times and seems to be random.

Anyone ever seen this?