In response to my query "How do I authorize a device" I received the following instructions.
"Make sure that this Adobe ID is the same ID that was used to purchase your eBooks. Also, if you are syncing an eReader device to Digital Editions, make sure that it's the same Adobe ID."
I bought the book I'm trying to read on my Nook Simple Touch from CBD, not from Adobe, so no "Adobe ID" was involved in the purchase. And how do I authorize my Nook to accept content from Adobe Digital Editions? The Nook shows up in my ADE library, and when I drag and drop a book onto it, the book shows up on the Nook. But I get an error message "User not activated" from the Nook.
I've already rebooted the Nook, deleted and restored the Digital Edition folder from the Nook and re-sideloaded the title from ADE, had reauthorized and re-authorized ADE, and rebooted the computer. Still getting the same error message.
MacBook Pro, OSX 10.9.5, ADE 4.0 (downloaded today), Nook Simple Touch