Incorrect email or password
You will see this error when you have entered your email address or password incorrectly, or the account does not exist. If you have forgotten your password you can reset it.
Account not activated
This error occurs when you have signed up using the sign up form but have not verified your email address yet. If the email has not arrived in your inbox (check your spam/junk folder) you can resend it.
Account not linked
You will see this error when you attempt to sign in with a Facebook or Google account that has the same email address as an existing account which requires email/password sign in and you have not linked the Facebook or Google account.