You almost certainly have one of the inks in the wrong slot. I don't know the R1800 inkset, but with my R300 it is quite easy to get the colours muddled in order and swap two over. If you do that, you get the message you have. If not, you may have bought a wrong cartridge type - some are very similar, but won't fit anything except the exact machine and ink slot intended. You can fit them physically but the printer will not work.