That is certainly related to the problem, thanks.
But following the procedure there, doesn't solve it. If I do this:
After inserting the image, press ENTER to create a paragraph break between the image and the text. With the cursor on the right-hand side of the image use the Insert -> Chapter Break command from the menu bar (or press CTRL-ENTER)."
Then save, then try to open the book with Adobe Digital Editions, it won't open.
This is with Sigil 4. With version 3, all is well. But I need 4 because it preserves the TOC.
Steve