Plutonium

Hamachi should work, although you need to install a broadcast fix for it to make the servers show up in the LAN server list.

I zipped it up, download here.

Firstly, you need to install NpCap (setup is included as npcap-1.60.exe) on your system once. Leave the option for WinPCap compatibility enabled.

When Hamachi is running and connected, do this:

1. Run HamachiBroadcastFixGUI.exe
2. Select your LAN adapter (Ethernet or WiFi) as the input device if it isn't already pre-selected
3. Select your Hamachi network adapter as the output device if it isn't already pre-selected
4. Click "Start"

If it works you should see the message "Broadcast packet forwarded successfully." appear in the log when you open a LAN game or server browser. And of course you should see each others' LAN games in the LAN browser.

Hope that helps!

Unfortunately I don't have a definite fix for this. I'd suggest you connect via Ethernet as well if you're at all able to. Make sure everyone has a direct tunnel to everyone else in Hamachi, not a relay tunnel. Also, switch around who's hosting, try everyone. I have the same error in my LAN and it will not work if PC1 hosts and PC2 tries to join, but it works flawlessly when it's the other way around.
Other than that, I can only suggest to search the web for other things to try.