Are you starting up with the Architectural Building Designer or the AECOsim one?
The Architectural one is the one you're looking for. As mentioned above, when you right click on it and select properties and you did a typical install it should show
"C:\Program Files (x86)\Bentley\AECOsimBuildingDesigner V8i Ss4\AECOsimBuildingDesigner\AECOsimBuildingDesigner.exe" -wsBB_DISCIPLINE=Architectural
If the -wsBB_DISCIPLINE=Architectural is missing you should add it to the appropriate shortcut and that should do what you want.
