Checksum error when trying to save.

[Hobie]

Hi guys, I'm completely new at this, I've gotten to the point where I've used PCM Hammer to open my OS which is 12209203. When I go into Tunerpro, make a few adjustments, deleting VATS, setting the max speed to 200, and taking out P0420 &430, then try to save it gives me a checksum error. I'm not sure if those adjustments aren't allowed, I'm doing it wrong or what. This is just a test PCM I took out of a junkyard truck, I'm trying to successfully complete these steps before I look into my swapped truck. I did save each item in each block before trying to save the whole program.