A limited number of titles on Ebook Central are not available for online reading, because they are in an incompatible format. These titles can only be accessed through Full Document Download. For more information on how this appears to patrons, see Why can't I read this book in the online reader?

If you are also seeing the Download Book button greyed out for these titles, your LibCentral Access Permissions Settings may be preventing the book from being accessible to your patrons. 
To resolve: If you do not want to change access permissions for all titles with that access model, you can update book level permissions: NOTE: All other settings restricting download are bypassed for download-only titles. Only the Download Days setting is enforced.