I've been designing a puzzle on Google Sketchup to be printed on shapeways. However, whenever I try to order, an error occurs. Apparently my design has "non fixable shells."
Unfortunately, this is the first time I have ever used both shapeways and sketchup, so I am at a loss.

If anyone is willing to help me, you can download the .dae file at: http://www.shapeways.com/model/250401/i ... tml?gid=ug
Just suggesting what to do would help!
Thanks
Andrew