Hello,
The B504 error would point to a problem with the hardware or there is an issue with one of the ink tanks. You can try unplugging the printer from the power to see if you can slide the ink over by hand or if it is locked in place. If you are able to slide the ink over, you can check if all tanks are seated properly or if any tanks are leaking.
If the ink is properly seated and you still get the error, it looks like the printer needs service. You can check your service options by logging into your MyCanon account or contacting support at 1-800-652-2666.
