Citroen C8 Auto Gearbox

Hi recently bought a 2003 2.0 petrol auto sx C8 luckily as a car for dogs and to use to go to our caravan (not tow) it seems to have an intermitant fault with the auto box all of a sudden. It flashes up on centre display "auto gearbox fault" with a beep, it then seems to pull away in what feels like 2nd gear from a standing start and you also can't use the sequential manual as it won't let you, if i pull over put the car in park and then turn engine off wait for 10 seconds and re-start the problem is rectifyed and all is good, it also seems to be within the first ten minutes of driving from cold, apart from that drives superb, any ideas please