Hello, please provide the printer model and cartridge model(s), and is it just 1 cartridge, or more than 1? The most common reason why a printer wont recognize a cartridge is if the chip on the cartridge is not making contact by the sensors inside the printer (where the cartridge clips in), so removing and reinstalling the cartridge can make a difference as it could be a matter of subtle positioning. There are other possibilities (such as a damaged chip on the cartridge, which would necessitate a new cartridge). But if you can provide more detail it is possible to better guide. Thank you.