Daniel:
The file converted in AC 16, but then an error message came up when trying to view it in the 3D Window "Invalid polygon, self intersection or hole intersects boundary. (fill grade porc)". The problem seems to be in the lower left corner of the Mesh: when I move one of the boundary nodes the Mesh gets fixed, then the node can be moved back. This can be seen in the 2D Window by selecting Floor Plan Ridges: Show All Ridges; the ridges do not appear initially, but will appear when the Mesh has been fixed, then the Mesh will show in the 3D Window.
David