This book was available temporarily on a eBook trial the library was holding called Patron Driven acquisitions. The message you received means that the funds allocated to that subject area have been exhausted, and therefore the titles are no longer available. These records will shortly be removed from the catalogue.
What is Patron Driven Acquisition?
The Patron Driven Acquisition service allows patrons to preview thousands of ebook titles that the library has not yet purchased. If the patron then selects to open an ebook, a purchase is automatically triggered and the item added to the library collection.