The ML1000 comes with 16 predefined ladder files. You cannot add more and you cannot delete them. Ladder 3 is reserved for the fault routine, 4 for the high speed counter interrupt routine, and 5 for the selectable timed interrupt routine (though if you dont use the HSC or STI you can use them for something else) and 16 is reserved for a debug routine. You also cannot change the data files or enlarge them.
I try to stay away from the ML1000 - The ML1200 is only a few bucks more and well worth it for the functionality.