Are both primary and secondary machine connected on the same local area network?
Can you try to ping the IP address of primary machine from your secondary machine (and vice versa) to check if both machines are reachable to each other.
Just run Command Prompt then type the command: ping 192.168.x.x
then check if it will receive a reply from the other machine
By the way, can you also tell us the current network connection type on both machine (wired/wireless/USB tethering/WiFi Direct)?