It is generally not recommended to put media files in the “Public” folder even though the WD My Cloud User Manual recommend it. The reasons for not using the “Public” folder are discussed in the [FAQ] Twonky DLNA Media Server Setup & Use thread. It is advisable to read that thread to understand some of the quirks of the Twonky DLNA media server.
Ensure your audiobooks are in a format that Twonky supports. This link has a general list of supported Twonky media file formats.
Ensure your audiobooks are properly tagged (metadata). If they are not Twonky may not display them properly. If one is using MP3 formatted files they can use a free metadata tag editor like MP3Tag to edit the metadata for their audio files.
Lastly if you have moved a large amount of media files to the WD My Cloud, it will take the device quite a bit of time, sometimes as long as 24 or more hours, to scan the media and update or build the Twonky media server database and the iTunes server database. If one continues to have trouble with the media files not being found, try rebuilding the media databases by selecting “Rebuild” under Settings → Media → DLNA Media Server → DLNA Database and selecting “Rescan” under Settings → Media → iTunes-> iTunes Database. Rebuilding the database(s) may take a considerable amount of time.
