Welcome to the modern factory stereo system. Both of those radios are VIN number coded. The BCM interrogates the stereo for information, if the numbers it gives back are incorrect it sets off the security lock in the stereo. It also can corrupt the programming in the ECM and BCM because it is a GM unit and it also stores information about the vehicle it came out of.
To correct it you need a factory scan tool, with it and a code from GM you can re-write the VIN information and re-flash the computers to make things work. You will need to take it to a dealer to have things changed, even then the stereo may not function if it was not an option for the 2002 model year.
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Monday, July 24th, 2017 AT 2:13 AM