Is it the triangle light that's on or is there a warning on the little screen?
Had this come up on the little screen once just after going on a dyno' not long after I got the car.
I think what caused it then was the front wheels doing about 100MPH and the rears being stationary, which might have made the ESP brain have a bit of a fart and a panic. A five minute pootle down the road and then turned the car off for a few minutes... Turned her back on et voila, no more warning. If there's no warning on the little screen reading something like ''ESP FAULT'' or ''ABS FAULT'' and just the triangle light is on on the clock then try pressing the ESP button (right of the wheel on the dash), it illuminates when the ESP is set to ''Off'' and you may have just pressed it without realising...
Failing that, it could be something like an ABS or speed sensor on one of the wheels having a bit of a 'mare?