If you are unable to download an eBook, the cause is normally due to a heavily firewalled internet connection, preventing the user connecting to the server from within the app. Downloading your eBook through your web browser often avoids this problem.
The best option is to do a manual download of the book. You can then add this to your bookshelf as long as you are signed into your Bookshelf account.
The manual download link for this title is http://inventory.vitalbook.com/books/<eBookPart#>.vbk
Once downloaded, move the file to the correct folder, which varies depending on your operating system.
Windows 7/8/10: C:\Users\Public\Public Documents\Shared Books\VitalSource Bookshelf\VitalBook Library
Mac OS X 10.4 or Later: Macintosh HD > Users > Shared > Books > VitalSource Bookshelf > VitalBook Library
Once completed, re-launch Bookshelf and access your book.