Ahh! Now I see, the problem is all the modules are coded to the main ECU, if you replace one the ECU sees it as an attempted theft so it puts the light on the dashboard and blocks fuel injection.
The way round it is to replace all of them with a matching set including the ECU and the matching keys from the donor car.
Or to get the ECU reprogrammed so it accepts a new set of equipment.
Luckily our CRD ECU is very similar to the same age BMW so a lot of the ECU repair companies can work on it.