Crum chip is on the back of the toner cartridge. I'm guessing a new toner was just installed. Sometimes you will get a cartridge with a bad chip on it. First thing I usually do is try a new toner. Or you should be able to swap the chip off the old cartridge is they still have it. I think that will work on the 277, I know it works on the smaller machines. The crum chip is, as I said, on the back of the toner cartridge. It is green and has two screws holding it on.
I generally pull out toner cartridge, check to see if there is toner still in cartridge, do reset TC 16 restart copier with door open, then reinstall toner. Have done this countless times and have only had one bad crum chip.