Common causes of this error are:
A firewall is blocking the connection to/from the remote machine on port 5151. Check your Windows firewall on both the Tutor and remote machine.
The IP address of the machine you are connecting to is invalid.
The computer name you are connecting to has a different IP address registered on the Tutor machine. This can occur when your DHCP server allocates a new dynamic IP address to a computer name but your DNS server has not been told about it. So, then your Tutor machine asks the DNS server for the IP address assigned to the remote computer name, then the wrong IP will be returned.