It is locked because the wrong Security Code has been entered too many times. What might work is to leave the radio switched ON for 12 hours or more ( undisturbed so overnight might be best) and that might reset it. Then reenter CORRECT code. If you do not know the correct code thenask another question quoting the Serial Numbers found on the radio casing..If this does not work , then it will have to be taken in to a Decode Specialist or the Ford Main Dealer for unlocking.
RegWorts
May 2008