Thanks! According to the log, this looks like some kind of connectivity issue. The client and server were able to successfully establish the FTP data connection and start uploading data, but later the data connection failed. From the client side, this manifested as a SocketException(0x80004005 / Connection timed out). From the server side, this almost certainly manifested in a similar way. However, the FTP control connection survived this - the server was able to respond with an error code (426 File transfer failed). This means that the issue might be caused by something along the way, and it's quite possible that neither the client nor the server are the real cause. We would like to look into this - I'll send you a list of possible next steps via email.