Error 10054 means that the connection between VPOP3 and a remote computer (eg the ISP or another computer on your LAN) was disconnected by something outside of VPOP3.
This is often caused by anti-virus software or Internet security/firewall on the VPOP3 machine but it could be any of a number of things. Any software or hardware that is sitting between VPOP3 and the ISP could be the root cause.
It could also mean that the remote computer itself decided to drop the connection abruptly, or that the network connection failed unexpectedly (or that the user dropped the network connection manually).
The only thing that is certain is that the problem is not caused directly by VPOP3, since Windows would give a different error code if VPOP3 was closing the connection.
The simplest way to diagnose the problem is to gradually turn off everything that could interfere with the connection, such as anti-virus software, anti-spam software, Internet security and firewall software on the VPOP3 computer, and to check any hardware firewall settings are not performing security checks on emails. Then, if the connection starts working at some point, you should know which piece of software/hardware was causing the problem, and you can contact the support team for that software/hardware for further help.
If you are technical, and understand the TCP protocol, you can set up a packet sniffer (eg Wireshark) on the VPOP3 computer to see if the connection is being dropped outside the VPOP3 computer or within it. You may also be able to configure logging on your router/firewall to see if the connection is being dropped there (eg due to NAT timeouts). We cannot help with these things under our free support.