I have a DX6050, and have had a similar problem in the past. Although I sourced my cartridges from the same (old) supplier, they appeared to be of variable quality.
Cartridges may fit, but they need to be chipped in a compatible manner for them to be recognised. Some older stock work for earlier models, but not for these printers.
The simplest answer is to break the bank, and buy Epson original cartridges.
The cheaper option is to buy a set of recently-made compatible cartridges, from a different supplier from your last lot.
I have more recently used More Inks click here for a while, and had no problems with the cartridge not being recognised.