One of the many features you get spoiled with using in Flex Builder is code hinting. Unforunately, this is one of the things that break when you start installing new sdk’s….if you haven’t upgraded your Flex Builder in a while that is. Here’s the link to the upgrade from 3.0.1 to 3.0.2.
If your sdk isn’t finding the flash.events.* package, it will remove them when it goes to clean up your import statements. It also won’t help with code hinting at all, but it will still compile if you manual type in the import. Very annoying, but fixed.