"Wrong Cartridge" I suddenly started getting this error "Wrong Cartridge" on Pixma Mp780. I changed all of the cartridges (oem) but it has not helped. I am disabled on on a very limited income so I really need to know what the problem before I start spending a lot of money I don't have to fix it.

There really aren?t but three options per Canon: -Reseating the print head -Replacing the print head -Press the ON/OFF switch to reset the device. Cleaning the pins as mentioned and trying new genuine Canon cartridges) are good to try as well; however, the next thing to check is if this printer is still covered by the warranty. If it?s less than one year old or if you?re not sure call Canon and see what they will do, it doesn?t cost anything except time. Everyone wants to save money on labor but the relatively small amount of money you?ll save you could easily loose by experimenting. I?m hoping you don?t flame me for this (I post to help, not make money) but a new print head is going to cost around $50 and might not even fix your problem. Unless you have access to a printer you can use for parts my suggestion is to not invest any money on buying parts unless you are absolutely sure the part will fix the problem. Instead I would suggest you have a local authorized shop take a look at it. Most will change a modest evaluation fee ($30-$40 that typically is applied to the repair cost) and they can tell you what it will cost to fix. Add to that the typical 90 day warranty as well.

Canon never released what caused this however it was NOT resettable or servicable. It affected around 1 in 3 mp780s & also similar units that used the same circuitry, needless to say tens of thousands were just thrown out & Canon got a get out of Jail free card but it didn't do the next couple of years sales much good.
Having said that, there is NO manfacturer that hasn't had a similar problem on a specific model at some time, naturally they don't advertise that fact.
Canon was lucky because many units failed out of warranty.
Happy printing all

Your print head is bad. You can purchase a print head straight from Canon @ 1-800-828-4040 and install it yourself.

Remove the ink cart and the print head for all of the colors. Reseat and reinstall all colors then run the printer maitinence. If it still comes up with the error, replace the print head. Cannons are known for the head problems. Hp and Lexmark always have new head with new cart to avoid this issue.

Ok, Now open up the printer where you put the cartridge, get a dry peace of cloth and start cleaning the metal pins that align to the printer cartridge. You may use some perfume to make more clean. This what have caused the printer to prompt "Wrong Cartridge" Good Luck