My printer (Epson RX680) first didn't recognize the cartridge, but I shortly found out the root of the problem and got it all working now!
The problem occurs when the cartridge didn't go all the way down into it's fitting, or when it pops up after not being held firm enough. The contacts on the cartridge don't meet those on the side of the fitting, making the printer report "cartridge error".
The solution is very simple:
After installing the ink cartridge, fold a little piece of paper (such as a post-it note) 3-4 times and put it right on top of the cartridge(s). Then close the ink door, it will be a little harder to close with the paper inside. Finish the cartridge replacement routine as usual, everything should work well now!
Works perfect, delivers color identical to the Epson's original ink. No colorsync problems, works excellent on both Photo Paper and CD/DVD surface.
CONS: The printer doesn't register this cartridges right away, but there is an easy fix.