Printing Problems with the iP4200

I wouldn't say it's a serious problem i have read other forum's and i think i know how to fix it but i would rather ask an expert

But for some reason when i try to print it comes up with a ink tank error, saying open printer cover and replace ink tanks on which ink lamps are off, my ink tank's are full nothing wrong with my printer, aleast i think,
I wouldn't know how to fix it so well yeah
Greatly Appreciate and answer =D
Tanks guys.....