Did this multiple times a day, did this multiple times throughout several days, still "Serial Number Unknown" and no OTA Updates.
Also, purchased it from Best Buy.com, got it the day after ICS was released, that was the first thing I tried to do, turn it on and update to ICS. Nothing! Wasn't rooted, since you cannot root a "Serial Number Unknown" tablet as much as Gary or Asus may want to hint that it is based on previous comments.
More of a suggestion, and far from a fix. The OP should update the title with a questions mark so it is obvious this is a suggestion and NOT a fix!