Yeah i've been having that problem too, but unfortenatly i havn't sloved it.
All i know is this: You have to save in a special way in Rhino when saving the DXF.
And also you have to remember that you dont have too many faces too.
Let me know if you get any help. Thanks!
/Zraii
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"Control unruly portions of the Galaxy through a fear of force, rahter than actual force itself."
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http://opt.alliacehq.org)