As far as I now vla-intesectwith works only with mathematical curve objects like : ellipses, circles, lines, arcs, 2dpolylines, splines, (3dpolylines - if another curve intersects with it). Helix curve is always 3d even if you enter its height to 0.0... If you want to find its intersection with 2d curve, you must explode it and modify spline control points to be on elevation 0.0...
See
this for more info
M.R.
BTW. vla-intersectwith can find intersections between xlines and rays (those are also mathematical curve objects)