One more thing you could try on the portable install:
- You will lose your customisations, plugins etc, so you might want to take a backup first
- With calibre not running, delete the folder <wherever>\Calibre Settings
- Then start calibre portable, it will create a fresh Calibre Settings. Then try viewing that Lucio Apuleyo EPUB.
- And let us know what happens.
If that doesn't work I'm baffled, bewildered, and out of ideas.
BR