Jason used ethanol (you can get "denatured" alcohol from a hardware store); I used isopropanol (rubbing alcohol). Both should work about the same. Set the print head, jets down, on several thicknesses of paper towel. With an eyedropper or with a Q-tip, appy drops of alcohol to the porous metal disks where the ink carts sit. It will pass out thrrough the jets and into the paper towels. Keep at it until no more color is seen. Jason let it air-dry for 24 hour, whereas I rinsed through some water and re-installed directly.
This will get the passages and jets clean, but the error messages are more likely to be electronic in nature. Try using a pencil eraser to polish up the golden metal contacts on the back side of the print head, and the metal nubbins that they contact in the printer. If that fails, the print head is probably dead and needs to be replaced. (The jets get very hot, and they can burn out if they run dry for even a few seconds.) I learned to keep a spare on hand after about the fourth replacement - they simply don't last forever. ($40 or so on eBay, which is where you can get good generic ink carts as well - G&G is a reliable brand.)
The print head is the weak link in the Canon design - burn out one jet, and you have to buy the whole array - but HP is worse: they make you buy a new print head with every ink cart. If you print a lot of color documents, Canon is much more economical, especially if you use G&G inks.
