Looks like "Unison available for free until tonight!" has expired.
Open your book in the calibre E-Book Viewer. Then right-click on a page that has the mysterious dot and select "Inspect" from the drop-down menu.
You might have a pointer to a jpg file that isn't there. Possibly one or more of the ornate chapter headings are not located where they're expected to be.
Just guessing without being able to dissect the sample of "Unison".