ERROR opening https://cactus.nci.nih.gov/chemical/structure/InChI=1S/C4H6/c1-3-4-2/h3-4H,1-2H2/file?format=sdf&get3d=True  -- InChI=1S/C4H6/c1-3-4-2/h3-4H,1-2H2 could not be loaded.