Can't Boolean-Combine PolyNURBSFit and non-design space parts

Hi everyone,

I'm currently larning how to use Inspire to perform topology opimizations but I can't complete one of my first jobs due to the issue explained in the title.

I performed an optimization with Stiffness target, min size=0.005m, and then used the Fit tool since the complicated geometry of the result made manually wrapping quite hard.

I tried multiple settings for Density and Break Angle, starting from default ones.

The nondesign space are hollow cylinders, I tried changing their thickness from 1 to 3 millimeters.

I always get an error saying 'Unable to complete Boolean operation' and sometimes the program keeps loading and freezes for hours until I can only force kill it from task manager.

Only hypothesis for the moment is the fact that non design parts are circular (hard to mesh?) and connect two separate regions the Fit istance is made of. 

Hope you can help me since this problem is stopping me from using the Software altogether.

Thank you very much