OpenSCAD render (F6) fails with "ERROR: CGAL error in CGAL_Nef_polyhedron3()" I built a model and it previewed correctly.  When rendering for STL export (F6), I got an assertion error:

ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion
violation! Expr: e-&gt;incident_sface() != SFace_const_handle() File:
/mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_S2/SM_const_decorator.h
Line: 329

Most of the model rendered correctly, but one component disappeared.
Moving the object didn't change the problem, but isolating just the disappearing part gave me a correct render of that part.
Reading between the lines on other forums, I found that the GCAL renderer will render a malformed object, but it will fail when a binary operator, such as union or intersection, is applied to that object.
There was a discussion about degenerate points (two points in a polygon list that were the (nearly) the same values.  I had this situation, but fixing it did not solve the problem.
I rederived the face lists, and found that for one face the vertices were listed in the opposite order from the others.  Rather then using right-hand-rule, I had used left-hand-rule.
Reordering the vertices for the one face fixed the problem.  There was no way to see the problem from the preview.
A more useful diagnostic message would have been helpful, or a tool for checking polyhedra for being manifolds could have saved me hours of experimenting and failing.