Problem with AttachGHSdata

I’m making a model of a ship with bulbous bow; as far as I can tell the section lines are fine. The curvy parts are splines and the straight parts are lines, and then connected. When I use AttachGHSdata, with the selection of curves (not shapes or surfaces), some of the curves are not included in the GHS shape, or are included wrong. What are some common mistakes in the lines that could cause that? All my sections are one continuous line and they all have the same direction.