Purchased books will not download onto new iMac.
I cannot download previously purchased books onto my iMac. Each time I get an error message that says the title has failed to download. "To try again, select Check for Available Downloads from the store menu." The store then tells me that all available purchases have been downloaded for this Apple ID. Some are downloading, but most of my purchases will not download. When they attempt to download, they will get to 1 second remaining and then I get the error message. iBooks then asks me "Are you sure you want to cancel the download of "title"? You can re-download this book for free at any time." There are two buttons: continue and cancel download. Continue cancels the download and cancel download tries to download it again. Frustrated and confused. Any suggestions?
iBooks 1.5
iMac 10.11.5, 4 GHz i7
8 GB
2.89 TB Free Space of 3.11 TB
iMac (Retina 5K, 27-inch, Late 2015), OS X El Capitan (10.11.5)