An update.. I disassembled the screen from the N9 and took off the battery cover and side bar. When I plugged the screen connectors back in, the phone turned on, with no error messages.

Once I screwed back in the battery cover and side bar & reconnected the screen, the same error message came up with the N9 was turned on.

I can't figure out what's happening once the battery cover is screwed down. Could it be it's not screwed down far enough so that the square pad isn't touching the chip underneath or perhaps the battery wires are being pinched? Any insight would be helpful.