Hi, I'm new to shapeways and I wanted to print out a ring, I uploaded a prototype of my ring (because it was unfinished), in multiple file formats to shapeways and they all gave the same error, empty output. But when I checked my model, all the normals are correct and I made sure to use a boolean operation on all parts. And finally, I used Netfabb to check and repair my ring. it came out correct, with no bad edges, 1 shell, no holes, positive volume, surface is closed, surface is orientable, and I exported it from Netfabb and uploaded it again. It still gave the same error, empty output. I'm running out of ideas here, can someone here just take a quick look at my file and tell me what is wrong with it?