Hi zolibaci,
Your PIXMA MG7120 does not read the amount of ink actually in the tank, rathe it reads a chip embedded in the cartridge which keeps track of how often it has been used. Refilling the tank does not reset the chip, so the printer will still read it as empty.
If you want to continue printing in this condition, you need to release the function for detecting the remaining ink level. Touch the machine's Stop button for at least 5 seconds, and then release it.
With this operation, releasing the function for detecting the remaining ink level is memorized. Please be advised that Canon shall not be liable for any malfunction or trouble which may be caused by continuation of printing under the ink out condition.
Note
If the function for detecting the remaining ink level is disabled, the ink tank in grey is displayed in the remaining ink volume screen on the touch screen.
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