There's a small toggle switch on the side of the cartridge bay assembly that reads the depth of the tab on the cartridge itself. Either you have a problem with that, firmware, or the chips on your carts.
You can replace the entire cartridge assembly in one shot, as it's ordered as a single piece, but if you can get away with it, I'd just re-seat the toggle switch sensor, and see if that does the trick. Getting to the cartridge assemblies is pretty easy if it's on the left side of the machine. If it's on the control panel side though, you have a bit of careful disassembly to do.
Edit:
Also, what Bobby said. Posted before the thread updated with his post.