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 !

I was trying to compile Hello Flash application in Flash CS3 and i got this

1046: Type was not found or was not a compile-time constant: WebService.
1046: Type was not found or was not a compile-time constant: HTTPService.
1046: Type was not found or was not a compile-time constant: RemoteObject.

Any Ideas ?