I'm assuming you want to make the file a solid as opposed to
just being a surface body. Is the surface just listed as being one
surface body or does the feature tree show many instances of
imported surfaces. How complex are the surfaces? There could be
many gaps between surface boundaries preventing the surfaces from
enclosing a "watertight" volume. If the surface has rather simple
geometry you can try try using the "Thicken" feature.
One way to find open boundaries is to look at the surfaces in
wireframe mode and look for edges that are a different color than
black.
Is the model small enough to post so we can see what your
dealing with?
