Hi Pedro,
could you solve it, as we have the very same problem? We actually tried the following, that partially worked: we exported (via Global Mapper) the shape file as GRID (x,y,roughness) and imported it in Map Editor as a grid. Map Edito is able to create polygons from it. This was partially succesful, despite in this way there are a lot of problems of discretization, and the precess is very slow ... so we are still searching for the possibility to use the shape file directly.
thanks
Antonio