That means the cartridge is not detected correctly. I recommend performing a reset of the printer. While the printer is on, unplug the power cord from the printer. While the power is off, press the power button 5 times. After 60 seconds plug the power cord back in and power on the printer.
If that does not resolve the issue, the printer would require service. The MB2050 is neither sold nor supported in the U.S.A. You've reached support for Canon U.S.A. If you require support outside the U.S., I recommend contacting the branch of Canon for your region. You may find the correct website using the map on the Canon Global website: http://global.canon/en/support/
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I tried the fix you recommended but it did not work. However I search on google and found a way to change the cartridge even though it wasn't showing low or empty and fitted a new cartridge and the question mark is now gone. Checking on old purchases of ink cartridges I see my printer is at least 7 years old so it is probably passed its best. Not sure what is a reasonable life for a home printer is.