Check the following points to resolve the issue:
If you are not using Genuine Brother Brand toner cartridge, the machine may not detect the toner cartridge.
Use a new Genuine Brother Brand toner cartridge.
The toner cartridge model number is not compatible with your machine.
Verify the cartridge model number will work with your machine.
Visit the Online User's Guide and Consumables & Accessories section on this web site to know what consumables are available for your machine and its toner cartridge model numbers.
The toner cartridge or the toner cartridge and drum unit assembly is not installed correctly.
Remove the toner cartridge and drum unit assembly. Remove the toner cartridge from the drum unit, and reinstall the toner cartridge back in the drum unit. Reinstall the toner cartridge and drum unit assembly back in the machine.
If the error message is not cleared, contact Brother Customer Service from the "Contact Us" section.