You should start from the basic steps:
1. Check the ECU sticker, Google the model number and check if the unit is compatible
with your vehicle.
2.if the unit is the right one for your car try to disconnect the battery for at least 15
minutes then connect your diagnostic machine to the car.
Make sure to use VIN detector first, if the same problem occurred then try to choose
the car model manually by selecting the model, if the problem still exist it might mean
that your car is remapped and the programmer has locked the ECU, in this case you
need a new ECU and your data should be cloned from the old ECU, or if you can find an
ECU specialist who is able to flush your existing g ECU and restore it to the default
values.

Best of luck.