So, I've worked, and learn a series of tutorials on Blender, and just to test, I've tried to export in Blender and import in LOTUS CT.
I've keep the most basic shape, export with all the needed options, but I've still the error 'Import not completely possible because Cube - the basic shape that I've talked about - is partially or completely untextured!".
I'm giving you my Blender File and the exported file, to try to find the problem... I'm going to be crazy with this error