We were having similar problems with my sister's nook,in speaking to B&N she had to downgrade her Adobe Digital Editions to version 2 to get it to copy and open on her nook. Just an idea...
How do you downgrade the edition?
First, make sure that both the Adobe Digital Editions and Nook are both activated. If not, try it again after they both are. My sister spoke to B&N tech who had her download the version 2.0.1 and install it, transferred her book and she was able to read it.
The links to the older versions: