If you ever need to access FlashVars from a MovieClip that you loaded
externally, make sure it has been added to the stage first. If it
hasn't been added you can access any of the variables. This isn't a
problem with the loading/root clip because the document class is granted
immediately access since it is the stage.
I usually don't have this problem except I was using a 3rd party framework that didn't wait for the ADDED_TO_STAGE or COMPLETE events before accessing those variables.