Hi Jacobo - someone else has written to me that Modo 601 seems to be using the LightWave v10 style orientation for vertex normals.

If you're using MoI v3 there are options for "Modo", "LightWave v9.6", and "LightWave v10" - if you set it to the LightWave v10 style does it then work ok for you in Modo 601.

- Michael