Because I have Firefox locked down, the BN buy buttons don't work for me on the basic pages. What I do to get around this is:
1) Login. I can't see the login pop up so I have to pre-login at the top.
2) Click 'Read Instantly' on the book cover
3) Once the book opens up, I click 'Buy' and it magically allows me to give them my money! What a concept!