Not sure but HelloFlash doesn't use any of those classes. Can you tell us anything about your installation?
Also, if you haven't already, try removing the PureMVC swc from your classpath, as Flash doesn't use it.
Flexunit and Asunit were added to the Classpath(Preferences), but why would they cause these errors to appear in a PureMVC project ?
Removed them and it is working fine now !