immobiliser warning light flashing
 

(1.8 gti golf 98 mark4 )
Over the past year I have this problem with the immobiliser light flashing on occassion.
It's not all the time, maybe only about twice a week but it will take quite a few turns of the ignition key before the light goes out and the car will then start then everything is fine.
I was advised that it will be the chip in the key that would be the problem, so I purchased one from VW but this has not solved the problem.

Could the immobiliser then be the problem or is there something else that could cause this....?