I have a used FX3 and I am trying to purchase new sounds from FoxPro, but if I try to enter what I assume is the serial number (sticker in battery compartment) it tells me that "There was a problem with the number you entered. Please try again or contact FoxPro". My question is A) Is the serial number located on the sticker in the battery compartment? B) Might the problem be that it is a used unit and already registered to the old owner?