How to split large tileset into multiple smaller ones?

I have a large tileset, 256 x 16,000 px, I need to split it into smaller sets. I used photoshop to crop it into 256 x 2304 but I get this…

[code]Runtime error: /Users/David/Desktop/test/lime-tile.lua:531: attempt to index local ‘tileSet’ (a nil value)
stack traceback:
[C]: ?
/Users/David/Desktop/test/lime-tile.lua:531: in function ‘create’
/Users/David/Desktop/test/lime-tileLayer.lua:779: in function ‘create’
/Users/David/Desktop/test/lime-map.lua:1422: in function
(tail call): ?
/Users/David/Desktop/test/main.lua:5: in main chunk [import]uid: 146992 topic_id: 26272 reply_id: 326272[/import]