Hi Rudy, v1 has some problems shelling surfaces that come to a "pole" like the rounded top of your piece there.

v2 has some changes to the geometry library that improve this, and over here using the latest v2 beta your object seems to shell fine.

You can download the v2 beta here: http://moi3d.com/beta.htm

If you want to shell this in v1 instead, you'll need to do it in a more sort of manual way probably by offsetting the profile curve for that rounded cap shape, and then making a new revolve with the offset curve for the shell's inner surface. Then that can be extruded and booleaned out from the main shape to get the same result. But it's certainly easier to use v2 instead.

- Michael