Please download last version BookLibrary(ordasoft.com/book-library-joomla-ebook-extension
) and update your version on your site, and try again add review.
But Pro version of BookLibrary better for you.
In Free version BookLibrary you may edit reviews only in every book, in Pro version - we have review Manager.
Also in Pro version - you may set from which users review will auto approve.
Also in Pro version of BookLibrary - we show captcha to all unregistered users