HP recently has released new firmware which is used with the HP Officejet Pro X451dn/X551dw/X476dn/X576dw printers. New firmware will make current printers not able to recognize third party cartridges with compatible chips. You will have to use HP Genuine cartridges once you upgrade your current firmware. All HP Officejet Pro X451dn/X551dw/X476dn/X576dw sold after Dec. 2014 will not accept current third party cartridges with compatible chips in the market.
We will have a NEW GENERATION CHIP for these models available expected by end of May, 2015.