attachMenu to a Layout

The following code returns an error:

var dhxLayout = new dhtmlXLayoutObject(“parentId”, “3L”);

// attaching a menu

var dhxMenu= dhxLayout.attachMenu();

dhxMenu.addNewSibling(null, “file”, “File”, false); <---------------------------Error message in this line

dhxMenu.addNewChild(“file”, 0, “file_new”, “New”, false, “new.gif”);

dhxMenu.setHotKey(“file_new”, “Ctrl+N”);

Error Message:

dhxMenu is null

Are you attach all necesary js/css files? (in )

That was the Problem. I forgot a javascript file.