ERROR opening https://cactus.nci.nih.gov/chemical/structure/InChI=1/C4H6O2/c5-3-1-2-4-6/h5-6H,3-4H2/file?format=sdf&get3d=True  -- InChI=1/C4H6O2/c5-3-1-2-4-6/h5-6H,3-4H2 could not be loaded.