I have run into this problem many times on Brother printers. Usually the box is only half full and the sponge used to absord the excess ink is mostly white. There is a trick you can use to remove the error code without replacing the box. You do run the risk of ink spilling out but if you only do this once it should not be a problem. Here are the steps.This ony works on certain printers. Use at your own risk.
1. press menu/set *2,8,6,4
2. Press 8 and 0 keys in order
3. Press Black Start several times until the purge or flushing count appears on the LCD
4. Press 2, 7, 8, and 3 keys in this order
5. Press stop /exit
6. press 99 to get out of maintenance mode.