Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
What is the exact message that you are seeing on the printer or the computer?
Ok, that means that the printer has not detected the second cartridge.
Cacn you try removing both cartridges from the printer and ensure the protective tape has been removed from them, and that the gold contact area is clean, then reinsert them again.
Let me know if that works?