Extend the lifetime of Brother MFC ink cartridges
To let your printer think the ink level is still sufficient for its services, you can trick the “light sensor” with black electrician’s tape on the ink cartridge:
Done, the error message should fade away and you’re able to use the printer again.
Note: In my case there was still quite some ink the cartridge to allow “ok” prints. You should replace the empty cartridge soon to prevent a clogged print head, though.