Got my pro today, "game validation error, update SD card" once I exited the initial setup screen. Reading the thread it seems one of the solutions is to just leave the machine on in attract for a while and it might/should clear. If it doesn't clear in a few hours I'll shut it off and re-seat the cards and power it up again.
edit: Took about 2-3 hours and the error went away. Leaving this here for the next person who has this problem.