This error means one of two things:
The username or password used to establish the secure connection is incorrect or not allowed
Connecting to a Mac
Ensure that you are using the correct credentials and that your Mac user is allowed to connect via the Remote Login service.
Connecting to a Window PC
Make sure that you use the correct username/password that was configured with your SSH server and that it is accepting secure connections
Connecting to a Linux PC or a Raspberry Pi
Make sure that a SSH server is enabled and that you are using the correct username/password.