I have attempted several times to open files that I've created and I am unable to open any of them. I have even attempted to create a new empty file. After I save and close the program I am unable to open the file again. Nothing out of the ordinary has happened (at least as far as I am aware).
Sorry that you've run into this problem! It is a known issue and we're working to resolve this. A simple workaround is to start the app first, and then drag/drop your designs in the application window.