Hello again, everyone.
There are a lot of really good threads on the forum for TCP clients. I too am making one that connects to a temperature chamber which is the TCP server. This chamber talks MODBUS.
Starting with this excellent thread's source code as reference, I was able to connect to the chamber and successfully send and receive packets.
That was last week. 
Today, oddly, immediately after the call to ConnectToTCPServer() succeeds, its callback function triggers with the TCP_DISCONNECT event type.
To double check, I've opened up the chamber's controller software, which connects to the server IP correctly, no errors. So I know the chamber is still up and alive. The computer is still functioning.
What else can I do?