multi_array_ref<> isn't default constructible. You need to let
Boost.Python know that:

  class_<boost::const_multi_array_ref<double, 2> > >(
    "const_multi_array_ref_2d", no_init
  );

  class_<boost::multi_array_ref<double, 2> > >(
    "multi_array_ref_2d", no_init
  );