MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
This design has the inner and outer shells both fused to the base. You can see this in the preview of the sliced object. Your cross section image shows the outer shell magically floating above the base, but in reality it is fused. The screwdriver separation trick does not work for me without destroying the lower grip. If you instead modeled many tiny weak support struts for the outer shell it might break free by twisting. As it is, this design (and the one it's remixed from) do not work with by printer due to how firmly the outer shell is fused to the base.