I am having a similar problem - after I download the book from the library, my Nook HD does not appear to the left in order for me to drag the book into it.
It appears that ADE does not support the HD+. I tried my old Nook Color and that still works. In looking at ADE supported devices I did not see the HD+. I hope ADE will fix this soon.
Thanks - but how am I going to get my digital library books?