Can you try removing the core's fqdn from the user name field?
Also, any real reason why you are creating a Preferred Server record for the core server? Are your packages pointing to the core server when you create them?
Can you try removing the core's fqdn from the user name field?
Also, any real reason why you are creating a Preferred Server record for the core server? Are your packages pointing to the core server when you create them?