Hi Kumsa,
HP Protected Cartridge allows the cartidge owner to set a cartridge protection, once a such is being set (probably by its previous owner) the cartridges will only be accepted by printer used to enable this feature and that cannot be undone...
You may find more information in the following link:
http://www.cartridgesupport.com/HP950and951usage.pdf
I would suggest contacting the cartridge supplier or replacing the ink cartridges