Hi Svetlana,
Thank you for the reply and context.
I just tried a test. Assigned 'Full Control' to the group accessing the plan on the parent folder and my book inherit permissions from this folder but still receiving the error.
From a security point of view, assigning full control to a user group (to enable the plan access without error) for a folder means they can edit/delete folders and assets. This seems like a security issue as we are only trying to give plan access.
Ronan