This happens due to – Incorrect Username / Incorrect password In case you have forgotten your password:

a. Click on the “Forgot your password?” link on the login page.
b. Enter your username and click the “Submit” button.
c. Enter the details of your “Date of Birth”, “City” and “Country” exactly as you had filled in the Registration Form.
d. Enter the answer to your “Hint Question”.
e. A new password will be displayed on the page. You can login to your account using this password.