I've found the solution on another forum. 'Lock 10' on my Ford fiesta 3000T radio cassette indicated that the incorrect code had been entered ten or more times resulting in a lock out.
However, you can get three more chances 'BUT MAKE SURE YOU HAVE THE CORRECT CODE TO HAND' or you're going to have to pay for it to be unlocked by a dealer.
With the radio on press nd hold the '6' button untill 'CODE' appears then you have three more chances, Use the keys '1,2,3 & 4' to enter your four digit code. then press the button '5' to accept the code. Good Luck.
DaveJ, December 2008