I have the same issue with my book, The Guardians of Time. I've e-mailed firstname.lastname@example.org about the issue, but they have yet to reply. I consider this a major "fail" on B&N's part. I have The Guardians of Time on the Kindle platform as well, and didn't have this problem.
For anyone else having this problem (as I was with my book The Guardians of Time), the following might be of interest.
I took my book "off sale" for a couple of hours, and then re-uploaded (1) the .epub file (first) and (2) the cover image (second). I then put the book back "on sale". It took a few hours for it to show up live on the B&N web site, but once it did, the cover image was finally available.
I don't know if the other problems are solved yet - i.e. the ability to download a sample or download the full book on purchasing it - which I've seen some other people referring to in other threads. But at least the cover image problem seems to have gone away after the steps mentioned above.
Best of luck,
Author, The Guardians of Time and The Sacred City