Int 6F Fn 12  - 10net - Unlock Fcb                                         [N]

   AH = 12h
   AL = mode
       00h sequential
       01h random
       02h random block
       CX = number of records
   DS:DX -> FCB (see INT 21/AH=0Fh)

Return:    CF clear if successful
   CF set on error
       AX = error code (see also AH=00h)
       0002h file not found

See Also: AH=11h