According to the Ford handbook , LOCK 10 means that you have had at least 10 unsuccessful attempts at entering the code, therefore it is now LOCKED and has to be taken in for recoding .
What might be worth trying is to disconnect the fuse or battery for 10 minutes, then reconnect and leave switched ON for at least 12 hours.(undisturbed ) This MIGHT allow another attempt to enter the code.(It does for other brands )
I assume that you know that the code should be 1515 ...unless it has already been recoded.
Please post back here whether you are successful or not
Good Luck !
RegWorts
April 2008