I released version 0.4.2 of Mark Book Builder. This version changes how image files are stored in the book document. Previous versions saved the path to where the image file is on your Mac. Starting with version 0.4.2, Mark Book Builder saves a symbolic link to where the image file is on your Mac.
This change is an improvement, as you’ll be able to move the images around on your Mac with fewer problems. But you may run into problems loading a book with images from an earlier version of Mark Book Builder. If you run into problems, remove the image tags from the book text and recreate the image tags by choosing Tags > Images from the menu bar. An image tag looks similar to the following: