There could be several conditions:
1) Entered the email address or password incorrectly.
2) If you signed up with Facebook, you will need to click the "Sign in with Facebook" button to log in.
3) If you still can't log in, you could reset the password. Click "Sign in" on the top right corner of our homepage, then select "Forgot Your Password", enter your registered email address. You may receive the reset password link in the mailbox and then create a new password with the link. Please also check your spam folder if you cannot received the reset link.