"io.netty.channel.AbstractChannel$AnnotatedConnectException: ConnectionRefused" while using LAN

When one computer opens a single player game to LAN, the other computer cannot "see" the opened game.

When I type in "localhost" for a direct connect, I get this error message:
io.netty.channel.AbstractChannel$AnnotatedConnectException: ConnectionRefused:

I have worked with AT&T to make sure the problem is not with my network. I have worked with Apple to make sure no other issues are at work. My firewall is OFF.

I CAN network my computers outside of Minecraft (with shared folders, etc.).