I have a canon pixma MX868 printer purchased in hong kong using ink cartridge CLI 821. i cant buy same cartridge in australia so purchased CLI 521 made for the canon pixma 860 which fits perfectly and has all the same serial numbers but the printer will not recognise the cartridges. is there a fix? i sought support from canon but they waffled on about different regions use different ink.

SOURCE: Refilled cartridge not recognised by printer (canon PIXMA MP210)

I held down the stop butten for five seconds and now it seems to work fine. Perhaps this could help you.

SOURCE: I need a tool to reset my canon pixma iP4600 ink cartridges

I found the only tool I have seen at this url. http://www.patronenhandel.de/shop/index.php/cat/c13943_Canon-Chipresetter.html It is a German company, but I was able to order the resetter from them with no problems. It has worked very well, but was a little expensive. part of the problem was that the US dollar and Euro were not at a favorable exchange rate when I ordered. I didn't get any answers to my emails to them, but when I used there site to order, it took about a week to get the device. It is very simple to use.

SOURCE: RECOGNITION OF GENUINE CANON INK CARTRIDGE

most probably has been damaged.

ink cartrigde is damaged due to followin causes--
1. over heating  of head due to bulk printing
2. mishandling the cartridge.
3. repeated refillings

try this if you want to use this cartrigde again, it may work
1.  clean the golden contact points with isopropyl alcohol of cartrigde as well as the cartridge holder
2. remove cartrigde and install again after some days

possibility of fault in printer is minimal, 

SOURCE: Reset Canon printer chip

you can override ink check status and manually reset it in drivers options

SOURCE: Coloured printer with black not printing?

Breath and Relax... this should resolve your problem.
Routine maintenance and keeping full ink tanks will prevent this problem, however if you have the problem you can resolve it by doing the following:
1. Clean your ip3000 print head using denatured alcohol solvent which can be purchased from most hardware stores. If unavailable, use 91% Alcohol (isopropyl alcohol (first aid antiseptic) which is available for less than a dollar at most Walmart pharmacy departments.

*Warning: You may want to use a pair of latex exam gloves as this is a messy process and can stain your fingers.

Supplies needed:
Isopropyl Alcohol or denatured alcohol
paper towels
latex gloves
sink, bowls and or basin
can of compressed air
very small screw driver
tablespoon or baby bulb type syringe
warm water
Time necessary 45-50 minutes

1. Lift print head from printer. It pulls out easily because it is held in with the same down lever that holds the cartridge in place.
2. Put two layers of paper towels in the bottom of a dish to protect sensitive sprayer heads.
3.Put enough solvent in dish to cover the screens on which the cartridges sit when in use.
4. Take the two small screws out that hold the white ceramic piece
5. Gently, pry the ceramic piece back and away , to reveal the underside (No need to pull away the glued points on the sides.)
6. Gently, move head up and down to slosh solvent around it the best as you can. Use a table spoon or syringe to pour solvent over all orifices in the print head, turning it upside down and then back a few times.
7. Use canned air with a plastic straw to blow into and through all orifices, alternately sloshing/swishing and pouring solvent over head (be careful not to touch any of the holes, screens, or sprayer heads with anything)
8. Empty dirty solvent from bowl and replace with paper towels and clean solvent. Soak for approx 10 minutes. Rinse again with clean solvent poured directly on all parts, letting solvent overrun and fall into dish or basin.
9. Gently shake the solvent off the head, take it outside and spray with compressed air into all orifices to clear out and help evaporate any remaining solvent. Let sit on a clean paper towel for approx 20 minutes. (There may be a little ink bleeding out of the head, but once it dries completely it does not present any problems.
10. Reinstall head, cartridges and it will print like a new printer.

SUGGESTION: For many years of problem free printing, keep a double set of ink cartridges, one set full at all times. Whenever a cartridge runs out of ink, replace it IMMEDIATELY, with a new one or a refilled one. This gives the print head no chance to dry out and create clogged heads. Routine maintenance of cleaning the heads every 24 months does wonders for keeping your ip3000 in new condition.

Happy Printing .