I just checked the DropBox, there are 5 tunes for 2002 Commodores there. I'm betting there's something behind the scenes that's causing these issues, I'd start with a bone stock, 2002 Commodore file and go from there. It wont give you the 12212156 OS, but 12225074 is a well supported OS as well. You can run COS3 with that OS and it is the proper base OS for your vehicle.

I dont see the 12212156 OS being used on any Commodore per the DropBox, however that could be incorrect as I've never seen one in person.