Unfortunately, the 7890/9890 and 7900/9900 are prone to print head problems (especially if they're not used regularly), and they have very different print head technology that can not be easily cleaned like previous model printers. There is some very helpful (and funny) information about these models here: http://myx900.com/
Epson has made it very difficult and expensive for people to maintain their printers, and we have found replacement print heads for these models cost around $2,000 from China!!
After reviewing your order history, I see you're using the 850ml model cartridges, which we have occasionally experienced chip read issues with due to physical cartridge fit. Below, I copied a related post from our forum, which I believe may resolve the issue you’re experiencing (the full thread can be found here: http://www.inkjetmall.com/tech/showthread.php?676-Epson-7900-ConeColor-Pro-inks)
"As you may be aware, we’ve had a few different cartridge designs for this printer model over the years (in search for the overall best cart), and we actually have a newer 350ml cart than the 850ml ones you have. The 850ml carts are great in many ways, and certainly fit/lock into the printer better than previous carts, but we started having an occasional fit issue with the last shipment, which effects the chip read, and I believe is what you’re experiencing. Unfortunately, the carriage manufacturer wasn’t able to offer us a satisfactory solution, so we continued searching for and testing other carts, which led us to the new 350ml carts we have. I can explain the issue that I believe you’re experiencing with the 850ml carts you have, and hopefully be able to get you happily printing. On top of the cartridge, where the chip is attached, some of the carts have a dip in the plastic, which can make the chip not have a good connection with the printer’s chip sensor. Raising the chip it’s self risks catching on the fragile sensor wires, so isn’t a safe fix. Several people have reported, and we confirmed in our testing, then taking a piece of typing paper about 4x6” and folding it lengthwise in half twice (so it makes a 1x6” strip), then placing it on the bottom of the cartridge bay while sliding the cartridge into place- this raises the cartridge up slightly, which is usually enough to make a good connection between the chip and chip sensor, and the carts/printer work great."
I hope this helps.
Best regards~ Dana