Annoying popup every time I print on HP 5940

Hello,

Every time I print something on my HP Deskjet 5940, a popup appears which
begins: "If you believe you purchased a genuine HP print cartridge" and then
recommends to go to some site to report counterfeit cartridges. I know I
haven't bought a genuine cartridge (but a valid compatible) so needless to
say this is extremely irritating - it means that if I print multiple copies
I have to wait there to hit OK every time. How do I turn this message off?

Regards,
Arfur