ERROR opening https://cactus.nci.nih.gov/chemical/structure/InChI=1S/C4H6/c1-3-4-2/h1H,4H2,2H3/file?format=sdf&get3d=True  -- InChI=1S/C4H6/c1-3-4-2/h1H,4H2,2H3 could not be loaded.