Connecting to a server using the Transfer Tool results in: Permission denied (publickey,gssapi-keyex,gssapi-with-mic)

Symptoms

When using the Transfer Tool to connect to a remote server, you receive the following error, where SOURCE_IP is the remote server's IP address:

The remote basic credential check failed due to an error (The password that
you provided is not correct, or the SSH key is not permitted access:
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).)
and response: Connecting to SOURCE_IP:22 as root...using method password...

Description 

This occurs when using "Password" as the Authentication Method in Transfer tool when the remote server does not allow password authentication in SSH via the following option in /etc/ssh/sshd_config:

PasswordAuthentication no

 This may also occur if you have disabled root login, which is a common security measure:

PermitRootLogin no

Workaround

• You can use an SSH Public Key instead of a Password as the authentication method:
  How to add or remove SSH keys for the root user
• You can enable password authentication in the SSH configuration of the remote server:
  How to enable or disable PasswordAuthentication in SSH 
• If the root login is disabled, you may want to re-enable root logins:
  SSH error: Permission denied - unable to connect as root 
• If enabling root login is not desirable, you can use a wheel user with root privileges to perform the transfer:
  How to create sudo users