Dave,
You may check also this:
"Drum Unit Detection Error" message after installing a new Extended Life Drum (DR315K).
CAUSE: Firmware prior to G00-V1 is installed on the MFP.
SOLUTION: Install firmware version G00-X4 or newer.
Another thought, check if drum units chips are there, if no/wrong chip I think it will throw that message.
As for Developing units TCR sensor is used for their detection...maybe somebody was trying to mess with chips?
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