Microsoft say this about Winsock error 10051 - WSAENETUNREACH:

A socket operation was attempted to an unreachable network. This usually means the local software knows no route to reach the remote host.

Full details of Winsock TCP error 10051 - WSAENETUNREACH:

Berkeley description: A socket operation was attempted to an unreachable network.

WinSock description: Almost same as Berkeley. For WinSock, this error is equivalent to Berkeley's EHOSTUNREACH error, the catch-all error for unreachable hosts. "You can't get there from here."

TCP/IP scenario: The local network system could generate this error if there isn't a default route configured. Typically, though, WinSock generates this error when it receives a "host unreachable" ICMP message from a router. The ICMP message means that a router can't forward the IP datagram, possibly because it didn't get a response to the ARP request (which might mean the destination host is down). Note: this error may also result if you are trying to send a multicast packet and the default gateway does not support multicast (check your interface configuration).

User suggestions: Try to ping the destination host, to see if you get the same results (chances are, you will). Check the destination address itself; is it the one you wanted to go to? Check whether you have a router configured in your network system (your WinSock implementation). Do a traceroute to try to determine where the failure occurs along the route between your host and the destination host.