You are correct - I just tested it and even after changing the German character it fails. We will investigate.
In the meantime you may try to import the Inventor file directly. We have enabled Inventor import for 2.1. It is still in beta, but it works. You will need to go to import and then select "all files" to be able to select the Inventor file.
Support will get in touch with you as far as the render resolution goes.