A common confusion can happen if you open a 2D Catalog while in a 3D Scene. If you do it will open the 2D Catalog in the Scene Catalog Browser. It is a common customer question that comes in, they want to know why they cannot open a specific 2D Catalog in the ICD Drawing. It is because it is already open in the Scene Catalog Browser. To fix this, go to a Scene, close the 2D Catalog. Then go to a Drawing and open the 2D Catalog from there. This will keep the 2D and 3D Catalogs separate.