Prius Died on the Fwy Today

The master warning light came on, followed by the engine check light, followed by the brake warning light - then the car lost power and stopped. I was able to restart it in about 5 minutes and thence drive it to the Toyota Dealership where it now resides. This is the second time the master warning light has come on in the car. Its a 2004 model with 16,000 miles on it. The first time it happend, the car had 4,000 miles on it - but the car didn't loose power and stop. The first time this happened, the dealership reprogramed the software. Today when I took it in, they indicated that they would probably do the same thing again.

Any idea why I'd be having this problem again after the dealership "fixed" the problem the first time? How can I trust that this same problem won't occur again some day when I have it out on a long trip?

What are your suggestions?