Cause
Rear tray paper information registration is incomplete. Or, the paper may have been exchanged while the printer is turned off.
What to Do
If the screen similar to the following is displayed on the printer's LCD, the cassette paper information registration is incomplete.

If the paper loaded in the rear tray matches the paper information displayed on the printer's LCD, select OK using the 
buttons and press the printer's OK button.
If they don't match, select Change using the 
buttons and press the printer's OK button. Then register the correct paper information.
If your product issue was not resolved after following the steps above, or if you require additional help, please create or log in to your Canon Account to see your technical support options.