So, I had ordered a #339 compatible print cartridge for my HP Deskjet 5940. It arrived today and I stuck it into the printer. A test page started printing, showing that everything was okay. A few minutes later, I tried to print a document, but OS X's print service popped up an error message explaining that the print cartridge was incompatible with my printer. A light also started flashing on the front of the printer itself. Wait, I'd just seen it print. Something was awry here. I took the cartridge back out, and stuck it in once more. Same error message. I tried again, only this time I decided to switch the printer on and off at the mains, then disconnect my internet connection before doing so. Once more, the test page printed, and the light on the printer stopped flashing. Little Snitch hadn't shown me any attempts to connect to the internet, so I tried using my Parallels XP installation and its own firewall. I blocked all attempts by any-HP related applications to connect to the net. Everything worked perfectly. Right now I'm sharing the XP printer and using cups on OS X to access it. The conclusion must be that either there is some kind of technical fault on the OS X side (which I believe is unlikely) or that the cartridge checks its status online, and stops working if it finds out that it's a remanufactured model. Anyway, finally I can print again! Do you have any similar stories, or suggestions?