I have the same issue... I created an account here for World of Tanks and got gems for that without any issues, tried reuse the account for World of Warships but got that exact error message. So created a new account by following the Play For Free link but still get that message.
in 3 steps
Choose the game that interests you and play itfor free.
Every game has some quests for which you will receive Soul Gems.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
You know that on Gamehag you can get real rewards for free, right? Join us, complete walkthrough and get your chest!
Why is this happening and how to solve it? I did all 3 battles and made an account