This happens to me all the time. I feel like I'm stepping hard enough on the brake, but must not be because the ready to drive light doesn't come on. I don't drive my car very often and I feel that maybe I haven't got used to the pressure required. It usually doesn't happen in my garage, just when I'm out running errands. Although it concerns me, sometimes I go 2-3 weeks between driving it (i have a commuter car that I'm trying to wear out) and I think it's user error.