Cobra, after having a similar problem, I just managed to fix it. I had assumed that the credentials for my Fidelity Visa were the same as for my overall Fidelity login. They are not.
First, go to
https://login.fidelityrewards.com/onlineCard/login.do and click on "enroll".
After stepping through that whole process including the ID shield steps, you'll have a username/login that is independent of your regular Fidelity login.
Second, login to your main fidelity account, go to full view, add account, click "I have an online login", the type Fidelity Rewards and you'll see "Fidelity Rewards Credit Card : ELAN CardMember Service" as your one and only search return. Click that, then enter the username + password you just created in the first step.
Hope that works!