Hello Friends, I'm a newbie to Blender, yesterday I had just installed it and studied something about 3D printing. The odd things is that when I create a mesh (a solid one) and I do the non-manifold check it always says that ALL edges are non-manifold, on the sample cube too. There is something I have misunderstood or missed? I have tried versions 2.49 and 2.53b (both x64), but the issue persists. Thanks for your help. Note: I have uploaded here a little .DAE example, an extruded triangle.