Individual surface, that's why :)
There's the tubes also but not the backface !

But I'm pretty sure that I tried to export the whole solid and it worked but it was too high polycount so I decided to do it with surfaces.
At this time I was on an i7 920 @ 3.5ghz and with 6gb of memory. It's better to export a cube before with low angle settings like 20° then export the solid, so that your exporter is set to 20° and not 5° for example !