FAQ: Why are some of the shapes missing?

Check the PDB file to ensure that the ring atoms are properly named. For most monosaccharides, they should be C1, C2, C3, C4, C5. If the residue is a sialic acid, the ring atoms should be C2, C3, C4, C5, C6, and O6.

Example error message from command line:

ERROR) vecsub: two vectors don't have the same size

Example image: