This problem is caused by incorrect login/passoword or internet connection issues.
We recommend to:
1. Check keyboard language. Check that Caps Lock is off. Read our password recovery guide article.
2. Check if firewall or antivirus blocks the game. Also, read the article.
3. Turn third-party programms off (such as torrent, Windows update, etc)
4. Write your login and password in a text document, make sure they are written correctly and there are no extra characters in them (for example spaces at the beginning or at the end), then copy them (Ctrl + C, Ctrl + V) into appropriate input fields in the game client.
If the problem presists, please, contact our Support Team. They will help you with this issue.