I put this in another post, I am not trying to spam. I have spent too much time frustrated with this ADE problem that I just want to make sure others get the message...
Here is a plan that works. I just did it on my Nook HD+. It requires a Dropbox account which is free and easy to set up.
1. Install Dropbox on your Nook HD.
2. On your computer or other device, put the .epub file for your book in a Dropbox folder.
3. Open the .epub file on your Nook HD.
4. Read and enjoy.
(It may prompt you to select which reader you want to use in step 3. Since I have the Books a Million reader on mine, it asked if I wanted to use that or the generic reader. Both worked to open the book.)