Data Tile handling sidescroller question

Recently I’ve been experimenting with mixing a tile based method of programming with the simpler art based method. By this I mean I’m making a mapArray that contains 800x600 tiles and loads them as the player progresses forward. (it keeps one loaded ahead and one behind the player at all times)

When i was simply placing in terrain it works fine. The player was able to run back an forth through the level with out any problems. However now i want to insert things like moving platforms. Previously when i was making it entirely art based I would type something like


and that platform would move to the right. However now that I’m loading the sections in on run time this path no longer works. At first i figured i could do something like


But doing so throws me an error saying “A term is undefined and has no properties.”

Can anyone think of a work around for me? If I’ve left anything unclear or if a similar question has been asked elsewhere please let me know.

Edit: (using AS3)