After reviewing your order history, I see you purchased the 750ml refillable carts in Dec 2011. So, you're saying the new 7890 sometimes doesn't recognize the cyan and matte black cartridges, or always gives an error with these carts? What is the exact error displayed on the printer's LCD panel for these two positions? Do you still have the Epson carts? If so, please install the MK and see how your printer responds (and if it gives an error with the cyan cart, if so what is the exact error), then install the Epson cyan cart to see how the printer responds.
It may be a slight difference in the printers, and the physical fit of carts. Have you tried a small wedge of paper under the arts you're having trouble with, to force them up slightly for a better connection between the cartridge chips and printer's chip sensors?
Please let me know, thanks~ Dana