You will get the error while authenticating when:

• You have entered incorrect password, used used non-authorized key, etc.
• The account you are trying to use cannot be logged in. This can be case even when you get “Access denied” only after entering password, as for security reasons, many servers do not reveal information about the accounts. Reasons for not being allowed to login include:
  • The account (username) you have entered on Login dialog does not exist at all.
  • The account is disabled.
  • The password has expired.
  • Number of parallel sessions allowed for the account has been exceeded.
  • You are trying to connect with super-user account (root), without having allowed that. Please read FAQ.

It may help to check log file of your server to see an actual reason, it denied you an access.