I had this problem for weeks now and already figured out what to do. It save a costly repair of $50 or $120 for a new balance board. If you encounter this problem, this means that sensor may have been dislodged for some reason. You need to re seat it. Remove the foot from each corner using a normal Phillips Screwdriver. - (keep them in the right order ) - Loosen (remove) the "stress sensors" small metal plate you see now at each corner using a "torx" screw driver. - Re-seat the small metal plate by putting it back but don't screw too tight. - Put the foot back on. Hope this helps someone in the future.
