ERROR opening https://cactus.nci.nih.gov/chemical/structure/InChI%3DInChI%3D1S/C4H4/c1-2-4-3-1/h1-4H/file?format=sdf&get3d=True  -- InChI%3DInChI%3D1S/C4H4/c1-2-4-3-1/h1-4H could not be loaded.