When I click on "Book here” from the benefits page, the page loads normally for me. I had to enter a valid pass number. Did you have to enter a pass number?

Does it help to clear the browser cache and delete cookies for eurail.com?

Thank you so much that has helped I can now get on - in order to get the discount do you need to add in a promo code ? 

As far as I understand, you need to click on the "BOOK HERE” button, which seems to use a special URL.