Actionscript 3 help needed

I am creating a game in Actionscript 3. The goal of the game is to build a city. The buildings in the city are on isometric tiles. The player can buy new buildings from the menu, when they do I want the building to snap to the tiles under the mouse pointer, until the player clicks a tile. I have tried but I can't get the building to snap to the correct tile. If you accept the challenge you will get my .fla to work with.