It happened to me once too, Internet connection broken for a while (for me) and then it fixes it next time automatically. Or your connection breaks up for few moments.
I can't really explain this. WSAENOTCONN is an error reported by the system when you try to use a socket that doesn't exist. But it's not LFS that closed the connection. It appears to LFS that your operating system just closed the connection without any reason or warning.
I don't know if it's your computer or your router or your internet connection or your ISP. The first thing to do would be restart both your computer and your router then try again. If you have another computer I guess it might be worth trying with that one.