I can't move the epub file from my computer to my Nook

I used to do this all the time, then suddenly one day it stopped working.  I've un-installed and re-installed ADE a few times.  I was getting authorization error messages, then got that to go away.  Now when I sign in I get an error

message that I have "No permission to copy the book" to my Nook, even though I've checked it out through my library's website.

If I simply try to open the document, I get an error message that the "vendor account you entered is not associated with the item you are trying to open. Try again."

I'm just going in circles and cannot read the books I've checked out.  Any help is appreciated.

Thanks!

Danielle