I have had the same issue. Every so often, on a random basis, my ESC light will come on when I start my car. Occasionally it waits until I shift into gear before turning on. In both cases, the ESC OFF button doesn't do anything, but usually if I restart the car it will go away.
However, it doesn't always stop, and I will have the problem constantly for a month, then it will be fine for three months.
Since I live in Hawaii, the weather does not change dramatically, so I doubt it is related. Unfortunately, the mechanic could not recreate the problem when I had it in for 30k service, so I don't know what to do.
Does anyone have an idea?