It would have been a good idea to post this report in the tool's main thread. I almost missed this. Without your problem SKP itself, then who can tell what's actually happening? Is it failing on every SKP or one in particular ? How does it 'crash' ? e.g. it hangs, it bugsplat, it shows a zero volume result ? It works fine for me. It is possible to devise two solids which when one is subtracted produces a non-solid. Since the API uses the Solid-tools as a basis, please try doing a manual subtraction of one from the other - make a copy of the two solids beforehand and also do the opposite subtraction if the first succeeds. There might be some tiny difference in the volumes creating ultra-thin slivers in the subtractions, thereby causing issues ?? Do you still have v2 to retry ? The licensing regime doesn't change with version. So reinstalling v2 over v3 will probably work ?