Not loading on to Kobo

Just bought a Macbook with operating system 11 so had to download digital editions 4.5 as 3.0 won't work with newer operating system. After getting many error messages, I found information on this forum to finally get books to download from public library to ADE 4.5.  I can download, open and read them on the computer.  However, I am unable to download books from ADE on computer to Kobo.  The books are listed on ADE as present on the Kobo reader, but when I disconnect the reader from the computer and try to open them on my Kobo, the cover of the book is black and I get an error message that e reader is not authorized to open this book.  I have erased devise authorization and reauthorized many times and each time it states the reader is authorized. I have done a factory reset on the Kobo.  I have also deleted and reinstalled the ADE 4.5 software many times.  I have erased computer authorization and reauthorized.   Any help are suggestions would be hugely appreciated!!