Getting to know Flash IDEs

I am trying to learn AS3 by downloading Flash Projects(open source), but can't seem to really grasp the right way to get the projects to run (through compiling) with IDEs (I am using FlashDevelop as an IDE). Here's an example:

http://www.flashkit.com/movies/Games/Shooting-manish_c-12372/index.php

Here's what I try to do:

1. I open a new Project on FlashDevelop
2. I copy all the folders to src, and make the main file(In this project it's called "rhymingRockets.as") as the Document Class.
3. I delete main.as (generated by default), and try to run it, but get the errors: Error: Definition fl.transitions.easing could not be found.

Click here to see the problem

Sorry for bothering you with such a simple question, but any help will be greatly appreciated, as I am new to Flash.