Epson P9000 not Recognizing Ink Cartridges?

We have 2 P9000 printers that are about 4 years old. We are starting to get a message that the printer is not recognizing the ink cartridge when replacing the old with a new cartridge. Sometimes reseating the cartridge helps. Other times I have to use another new cartridge. Other times when replacing one new cartridge, the printer will not recognize any cartridges. I usually resolve this by powering down and restarting. Is anyone else experiencing this or having these issues with their Epson P9000. We are using GMG as our RIP. Thanks