Here is a pretty simple part. I uploaded it 2 weeks ago and it was rejected for "inverted normals". Strangely, this week I uploaded exactly the same file and the error I get is now "Only manifold objects can be printed." MiniMagic claims the part is OK. A friend ran Meshlab on the part and found no problems with it. This file was created by another piece of software, and we don't just want to fix the part. We want to know what is wrong so we can fix the program that exported the file. Can anyone help? Please don't just fix it, can you tell me what is wrong? Thanks in advance for any help!