I am very new to Shapeways. I'm trying to create a model in Sketchup with all manifold objects and I'm having trouble. I want to be able to create my file in Sketchup, Export as a .DAE file and then upload to Shapeways, however, I get the non-manifold objects message every time I try. It's a fairly simple model. I have attached it. Could someone take a look and show me why I still have non-manifold objects in my model? Or offer advice on how to get rid of them in Sketchup? Much thanks in advance.