In the conceptual mass environment / Adaptive components, when you select a path element and some profiles (or one), there is no way to tell Revit which is the path. Quite often Revit will make the wrong assumption and fail to create form, with a message about 'self-intersecting geometry. I realise that this was probably intended to keep the UI simpler, but actually it is counter-productive. Please change the Create Form command to allow nomination of path
