Hi, A firend who is currently creating some designs for me has sent me the finished designs as .stl attachments in an email. However when I try to open them to upload I get the error message: Invalid Public Key Security Object File This file is invalid for use as the following: Certificate Trust list Can someone explain what is happening? I have looked this up elsewhere on the internet but the answers aren't really helpful. (It might be caused by the fact that I don't have a 3D program on my computer, but I would of thought it could still be uploaded to Shapeways regardless. When I try to upload it I can't because a youtube video appears in front of everything and the close button is not there so I can't get rid of it).