Brakes Failed problems of the 2004 Toyota Prius

I purchased a 2004 Toyota Prius new in June of 2004. In the last month I have had 3 incidents where the brakes failed while driving. Suddenly the brakes go to the floor, the car loses power and the warning lights go on. The last incident also included a high pitched tone which persisted until the car was shut off. The first incident happened on Nov. 19, 2009. I was driving at a low rate of speed and noticed a slight hiccup in the engine while turning a corner, then about 500 ft. Later, the warning lights went on and the brakes went to the floor. I shut off the engine, then turned it back on and drove slowly to the side of the road with the warning lights on and called my dealer, who told me to have it towed in. They had the car for 3 days, and replaced the abs ecu with actuator, the actuator assembly and brake for a total repair bill of $3383. 69. On December 22, 2009 the same sequence of events occurred in the morning. I was able to drive the car home at a low rate of speed with the warning lights on, then took it to the dealer, who could not find the problem and told me to bring the car back next week. Later that day, the car experienced the same brake failure while driving at a low rate of speed. I had the car towed to the dealer. They now tell me they cannot find the problem and the car is not displaying the warning lights at this time. They plan to keep the car for a week or so to see if they can duplicate the problem. I have a 50 mile round trip commute to work on the freeways of southern CA. If the car dies on the freeway in rush hour traffic an accident would likely ensue. The dealer has treated me very well through this, but I am concerned that they are unable to get information from Toyota to diagnose this problem. You have one other complaint for my model year with this same problem. Surely there are others, as I have seen similar postings on the web. Toyota must know about this defect, which I will bet is a programming error.