I got this same error message on a newly acquired Brother DCP-7040 that I purchased used off of ebay.
As I was troubleshooting this unit (that I bought untested off of ebay - hey gambling has paid off handsomely for me many times before!), this error message kept popping up.
I checked the COUNTERS (page & Drum life) and found out that the DRUM had 0% life left. BUT, the reason it showed ZERO was because this unit did not have any drum! The toner cartridge (TN-360) needs to sit WITHIN the drum (DR-360) on this DCP-7040 unit, as well as in models DCP-7030, MFC-7340, MFC-7345C, and MFC-7440N.
So perhaps some of these "put the black toner cartridge back in" problems could be related to the DRUM (or lack thereof). A possible tipoff (since the toner cartridge actually does slide into the unit much like other units that do not use Brother's DRUM carrier) seems to be the relative ease with which the toner cartridge slides into the DCP-7040 and really doesn't seem to "lock" into position real firmly.
DCP-7040 USER GUIDES: http://welcome.solutions.brother.com/bsc/public/us/us/en/doc/manual_index.html?reg=us&type2=-1&prod=dcp7040_us_as&c=us&lang=en&flang=all