#3D Lofter/Fit
Hard to tell what the problem is without actually seeing the project. However,
I'm guessing that your Fit shape (being stair steps) has horizontal lines.
These cause problems because they send an ambiguous message to the Lofter,
which may or may not treat them as undercuts. If this is the case, you can fix
things by moving one of the vertices for each horizontal line slightly so that
the line is diagonal. Note the word "slightly." You just need to adjust the
vertex a bit so it's not aligned with the other end of the line.
If this doesn't do it for you, you can send a .prj file for Jonas to take a
look at.
– Jack