Blocks have been directly created under a Section title, which causes errors in the outline pane.
According to the Information Mapping Methodology, Blocks and Maps are inherently linked, which means that Blocks are always part of a Map.
As FS Pro does not detect a Map title, the Blocks are referred to as errors.
Go to the 'Headings' group in the FS Pro menu and choose the option 'Section title with Overview Map'.
Put your Blocks under the Map.
Tip: You can change the Map title 'Overview' by a Map title of your choice.