Hi Chris,
What version of Ghost do you use (from the message it looks like GSS 2.0)? And what OSs are used for the Console and Client?
There is couple of causes for this to happen, one very common thing is a firewall is blocking the communication between Console and Client. For some firewalls we add the rules automatically but you need to add them manually for the others.
If this is not the case, it could be due to the network infrastructure. Do you have these machines in different subnets by any chance?
Krish