Presumably your laptops have both an Ethernet connection and a WiFi connection. Try building with WiFi disabled and see if that makes a difference.
In order to activate, the operating system needs access to either your KMS server or to the Internet for a MAK key. I am speculating that once the laptop is fully built and boots up, the activation process may be trying to take place over the WiFI connection rather than the Ethernet connection, and I would assume there is no valid WiFi connection as it has not been connected to a wireless point.