DrinkWine.mxml is my app , ---------DrinkWineStartupCommand.as ; StoreMmodule is a module in this project; Content.mxml is DrinkWine`s subComponent and reflect "ContentMediaor", PopupStore is my custom popup window reflect "StoreMediator",and the PopupStore include a canvas names "moduleContainer", i load the StoreMmodule in ContentMediator then send a notification contains this moduleLoader to StoreMediator; The StoreMediator can receive the moduleloader as "note.getBody() as FlexModuleLoader" now; and i register the DrinkWineMediator and StoreMediator in DrinkWineStartupCommand together at first, now i got a error " Error #1009: Cannot access a property or method of a null object reference " does this error means i cannot register two mediator as the same time in DrinkWineStartupCommand ?