The E6 error is a prize or payout error. That means the machine paid out an extra token. Usually the machines freeze and plays a tune to bring the attendant. You need to open the door and push th small reset button on the back o th door to cleart.
When the display is on the door indicates an error condition, open and close the door to reset the game. Then open the main door which clears the current game information. By closing the door resets the game and the reels will spin. Then the error code will get clear.