ECU repalcement on 2001 Saturn SC2

I replaced the ECU and now the car will not start. All the numbers match the old ECU. I put the old one back in and it will start. What may cause thisissue with the new ECU?

Asked by for the 2001 Saturn SC2
It is possible that it needs programmed upon installation. You may want to consult a Saturn specialist.

Here is a link to some shops near you... https://repairpal.com/directory?address=23231&car_brand_names=Saturn