I think I know what the problem is.
In our Cad system all elements that we need are choosen from a catalog. We design pipelines, and all elements are standard items. But that means that in fact the model is not one closed shape, but a lot of closed shapes together. Now sometimes the circular face of an item is shared with that of the item next to it. And this confuses the system that much that it doesn't see some of the items anymore.
Problem is that I am not designing for 3D printing, but have to convert a system 'as it is' to a model that can be read into the shapeways system.
Second problem is that the model I want to print is already quit complex, so I will always be in doubt if I really have fixed everything.
But if I get it working in a relative simple way, it would be very promising for future models to be 3d printed.
I am working in the Process Industry, and sometimes clients really want to see what we design.
We have 3D viewers, but keeping it into your hands really adds value to it!