Cherokee 2003 2.8CRD Engine Problems?

Hi

I have a Cherokee 2003 2.8CRD, over the last month the car has developed a problem of 'switching off' at traffic lights or when I slow down, I am guessing it may be an engine immobiliser problem ? - after 20 mins it starts again and off it goes for another 20 mins or so, the red light is on the dash board.

Any thoughts ?

Thanks

Matthew