Hi klego - well your bottom piece there is an open surface and not a closed solid, so the direction of its surface normals may be pointing in the opposite direction from what your program needs.

Some programs only render one side of an object. Sometimes there is an option though to turn on "double sided" rendering to stop that so check for any option like that.

Otherwise, you have a couple of other options - if you make your object into a solid volume in MoI instead of just an open surface type object, then it will automatically get its normals oriented towards the outside of the volume when you do the export.

The other option is that you can run the Flip command on an open surface object to reverse its orientation and when you export it after that the exported polygons will be oriented in the other direction.

Try the attached version of your model instead, does it work better for you? I ran the Flip command on the bottom object for that one:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#flip

- Michael