UPNP_E_SOCKET_WRITE signifies an error writing to a socket. This occurs in any function that makes network connections, such as discovery (e.g. UpnpSearchAsync or UpnpSendAdvertisement), control (e.g. UpnpSendAction), eventing (e.g. UpnpNotify), and HTTP functions (e.g. UpnpDownloadXmlDoc).