For HP 61 or HP 61XL ink cartridge error messages (i.e. "Cartridge Error", "Incompatible Cartridge", etc.) and the inability to print to the HP printer, this type of problem could be an electrical connection issue between the printer and the cartridge (i.e. dirty electrical contacts on either the cartridge or printer carriage flex cable surface), or more likely, an internal micro-electronic failure inside one of the HP 61 ink cartridges (please note it is very rare for both ink cartridges to fail at the same time - hence one of them is likely causing the current issue). NOTE: If the printer is stuck on the message "Non-HP Cartridge" or “Very Low Ink” and cannot be bypassed, this is another indication that the cartridge may have suffered an internal electrical failure.