Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I would advise you to try, first, logging out of the site that you got the show from (or, that you purchased the show from), on your Nook.
Then restart the Nook.
Then, when restarted, log into that site again.
Then try downloading the show you purchased from that site. If it doesn't work, check your email for a receipt for the purchase, and otherwise make sure that the purchase has actually been made.