I Began using Adobe's Flash Builder 4 Beta and started coding Actionscript code; I imported classes and at time intervals, Flash Builder 4 beta deleted my unused imported classes. It was really annoying since I imported all of the classes I need in the project. I think that the Flash Builder 4 should have this option turned off by default. I searched around the internet and found this to fix it. GO TO: Window -> Preferences -> Flash Builder -> Editors -> Actionscript Code. Uncheck "keep imports organized". See the image below. Hope it helps someone.