Hello there OBE17,
I have a couple of recommendations for you. First I would try deleting one of the audio books and re downloading it from iTunes to your computer. Use this article to help redownload it:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
- Open iTunes on your computer. (You can download the latest version of iTunes here.)
- If you're not already signed in, choose Store > Sign In, and enter your Apple ID and password.
- After you've signed in, click on the iTunes Store button located in the upper-right of your iTunes library.
- From the top navigation bar in the iTunes Store, click on the content type you're looking for (Music, Movies, TV Shows, Apps, or Books).
- Click Purchased located in the Quick Links section on the resulting page.
- From your Purchased page, you can click the tab for the content type, if you would like to download other previously purchased items (Music, Movies, TV Shows, Apps, or Books).
- Click Songs or Albums to change the page view and All or "Not in My Library" to view your purchased content that currently is not downloaded on your computer.
- Click the download icon to the right of each item to download that item.
Note: If you want to download previously purchased items that are already in your library, you'll need to remove them before the download icon will appear. Learn how to delete an item from your library in iTunes for Mac or Windows.
- To download previous purchases on a computer, your computer must be authorized for the Apple ID that was used for the original purchase. For more information about iTunes Store authorization and deauthorization see,this article.
- Books you purchase on your computer may be downloaded to your iOS device as well as your computer, but you may only read them on your iOS device. If you have auto-download turned on for your iOS device, books you purchase on your computer will download to your iOS device as well as your computer, but you may only read them on your iOS device.
- If they are offered for purchase in 1080p, you can download previously purchased 720p HD TV shows and movies in 1080p. Learn more about downloading in 1080p.
- Previous purchases may be unavailable if they have been refunded or are no longer on the iTunes Store. Downloading previously purchased movies and TV shows requires iTunes 10.6 or later.
- It is recommended that you always back up your iTunes library in the event that a purchased item is no longer available on the iTunes Store. For more information about backing up your library, see this article.
If the same thing happens with that download you may want to see if it happens in a new library as well after you download the audio book to it. To create a new iTunes library use this article:
iTunes: How to open an alternate iTunes Library file or create a new one
If it works fine in the new library then I would recommend recreating your library using this article:
iTunes: How to re-create your iTunes library and playlists
All the very best,