It is possible to create empty shapes that break the ImageMap

Repeat:

1. open ImageMap macro editor (or create new)

2. choose 'polygon' (probably happens for other shapes too)

3. click on the image in the Shape Editor

4. repeat until you have a clickable area listed on the right-hand side toolbar but no matching (highlighted) shape in the Shape Editor

-> saving the ImageMap now without deleting the empty shape (trash can on the right-hand side toolbar) will create a broken ImageMap that cannot be loaded to the editor