Tech was a typo. It's been three, and one was straight from Mimaki.
Cartridges will go out before their date or when they're used up. The Machine will report that the cartridge is wrong (despite being in the machine for quite some time), literally giving the error message "WRONG CARTRIDGE". This is not one color, but system wide. It is random, and it is speeding up. I used to think it was that the cartridges were old (often times it was the case, but not recently). If a cartridge is replaced, the machine is up and running.
Solutions that have been giving (aside from techs sitting dumbfounded, saying "WOW!" and telling me they've never heard of it):
-The brass spring clips on the cartridge sensor need to be bent back (Mimaki said this did not need to be replaced). We've taken the machine apart to check this out, did bend them back into place, and still had a cartridge go out.
-The contact on the chips may need to be scuffed (literally with a pencil eraser and alcohol) to reset contact. This did not bring back the cartridge.
We've tried to test our own theories: If we place the cartridge somewhere else in the machine, it comes with an error: "COLOR OF INK", as it should.
The sensors may need to be replaced, despite what Mimaki says, but this would be for all six colors; I'd buy replacement a bit more if it were one color or one side that was having problems). I'd also blame the sensors if we weren't back up and running with a new cartridge and new chip. This is why we're looking for a way to reset the chips we have, or acquire replacements. I have been able to find a couple of places who will sell replacement chips, but am unsure of their quality.