ERROR opening https://cactus.nci.nih.gov/chemical/structure/InChI=1S/C4H6/c1-4-2-3-4/h2H,3H2,1H3/file?format=sdf&get3d=True  -- InChI=1S/C4H6/c1-4-2-3-4/h2H,3H2,1H3 could not be loaded.