Make sure you create an GAME account and not forum account, go to
https://en.nostalrius.org/ and click "How to play" make an account there with an VALID email adress, go to your email and activate the account via the validate link you get there, there should not be a problem after that, next step is if you're using Norton anti-virus or any other firewall, try to deactivate them and try logging in again.
Best regards
Neelo.