Quoted from Vespula:

I was just reading about this one through searching because I had this pop up for 1 second during a game and go away not to be seen again.
Looks like its overwhelmingly pointing to the little black micro USB cable in the board under the playfield.

Quoted from atg1469:

pressure on the LED board and that black mini-USB cable that Vespula was describing.

Quoted from atg1469:

I do not have a photo but it's very easy to find. If you lift the playfield all the way up, the LED board is on the very back left hand side of the game. It's the one with like 10 ethernet cables plugged into it around the board, pretty hard to miss! The mini-usb is located on the bottom right hand side of the control board.
Again, others have mentioned that the mini-usb had a loose connection on their games and they were able to correct the issue by simply making sure there was enough slack on that chord, but that was not the case with my machine.

Quoted from Dexter:

Thanks so much!

Quoted from atg1469:

I do not have a photo but it's very easy to find. If you lift the playfield all the way up, the LED board is on the very back left hand side of the game. It's the one with like 10 ethernet cables plugged into it around the board, pretty hard to miss! The mini-usb is located on the bottom right hand side of the control board.
Again, others have mentioned that the mini-usb had a loose connection on their games and they were able to correct the issue by simply making sure there was enough slack on that chord, but that was not the case with my machine.