https://docs.microsoft.com/en-us/windows/desktop/winsock/windows-sockets-error-codes-2 says, that the cause of #10057 is
A request to send or receive data was disallowed because the socket is not connected and (when sending on a datagram socket using sendto) no address was supplied. Any other type of operation might also return this error—for example, setsockopt setting SO_KEEPALIVE if the connection has been reset.
As a programmer I know what it means - I should bind socket (via connect or accept API commands) before trying to call any further (e.g. send of receive) operations on this socket. As my implementation uses Delphi Indy libraries, I am aware of the problems with connected function https://stackoverflow.com/questions/5852359/tcpclient-connected-problem-in-delphi-indy . But I am already controlling all that in my software and it works great in many network environments. But one local network access almost constantly (in 90% of cases) generated #10057 error.
So - it can not be programming error, it should be something with network setup. So - my question is - how can I troubleshoot network for catching #10057 error?
Maybe antivirus is blocking application or access of application on that port and such manifests appears as #10057?
