OK now the next issue... SketchUp can't cope with the creation of very tiny edges/facets. It's built to model 'buildings' and all of their related accompaniments - up and down from that - so objects <0.1mm or >1km will ofeten cause issues... I should have guessed from the '1 to 1250' If you are making 3mm slices though a small object some of them will probably fail because they are so tiny that SketchUp considers them to be non-existent because their starts and ends are so close together ! These issues occur in native tools as well as API based scripts... Try doing a native FollowMe on a tiny face around a small/tight bend - you'll get missed facets etc... In SketchUp you should usually model at 'full-size' which can avoid many of these issues... Later on scaling a larger object downwards will work - because tiny facets can exist BUT it's initially making them that is the issue... Here's my suggested fix... [Work on a copy of your SKP!] Let's say we'll scale this up x100 and retry... Draw a line 10mm long. Use the Tapemeasure tool and pick the two ends of the line in turn, the VCB should say '1'. Type 1000mm at the keyboard [i.e. x100 bigger]. You are prompted to rescale the model. Answer Yes. Zoom Extents to see what you have. Now your model is x100 bigger and far less likely to mess up when Sliced [or even when any native tool is used on tiny geometry!] Do the Slicing - making the spacings/slice thickness x100 more to account for the temporary rescaling of the model... When it's done you now use the Tapemeasure tool, picking on the same line... but this time you type in 10mm and scale it back down... The tiny facets will now remain - they can exist but it's making them that can prove difficult... Report back...