This error appears during a login attept, when you have entered a wrong username and or password.
The reasons for the error might be one of the following:
You didnt fill in both the username and password fields.
You have mistyped either the username or the password - please keep in mind that both are CASE SENSITIVE, and also check for leading or ending spaces - sometimes when you copy from your email client you might have copied together with a space at the end.
Please also remember, that the Password, that was provided with the Welcome-E-Mail is single use only. You might have used a outdated no longer valid password.