Don't mean to dig up old threads as the problem is relevant.
Recently had same problems as described after a year of ownership. Warning comes up for less than 30 seconds and goes off.
Opened the panel and found that all the brake light bulbs were loose.
Push the light bulbs back in until you feel it clips on.
Been about 2 weeks or so, no warnings so far. Might be worth looking at before you book your car in.