Hello I am new to 3D modeling, and have only been using Blender for a few months. I am also new to 3D printing. I made a ring in Blender and I think I have followed all the steps on the tutorial page for prepping Blender files. When I export my .blend file to .stl, I notice it is called a "Certificate Trust List"... which is weird to me since the extension is .stl. Anyway, I upload it to Shapeways and I get an email notification that it is an "Invalid Input File Format", so I did some forum searching and read that I could download "Netfabb" and that it would "fix" any problems. Well I downloaded it and when I try to open my .stl file it too gives me an error "Invalid STL file" So what the heck is going on? haha Thank you for reading!