MP,
What Printertech101 stated is what is in the repair manual.
This message appears and printer is stopped when the ink supply pump motor drive home position in the ink supply air system (unit) is not detected within the required time at power on initialization or ink supply.
I would check your air supply motor, it should run to inflate the ink carts when you turn on the unit. It is pretty obvious as you can hear it running, or pull the control pannel side cover off, and it should be right on the end of the printer, the one with the ink tubes connected to it, with no ink in them.
When I was getting mine operational, I had bumped a connector, which caused it to not start, and got this error.
John