Ebooks are sold to libraries in a different way than they are sold to individuals. Unfortunately, AU Libraries cannot always purchase an unlimited-use ebook due to licensing restrictions. In those cases, you may have to wait for a classmate to finish using the book before you are able to access it. Sometimes you have the option to add yourself to a waiting list and be notified when it is your turn, but if not you may try again later. Reach out to a librarian if you need additional help!