FluentFTP EPSV Error 425 Can't open data connection for transfer of "/test.csv"

Question

I'm trying to upload a file with the .NET Library FluentFTP using EPSV connection type because I'm behind a HTTP/1.1 proxy and data and control FTP IP addresses are different.

Unfortunately I get the following error when calling the UploadFile method: Response: 425 Can't open data connection for transfer of "/test.csv"

The same operation works in FileZilla Client with the same proxy settings, so it can't be a network problem. This is my code:

using (FtpClientProxy client = new FtpClientHttp11Proxy(new ProxyInfo() {
    Host = "prox.corp.company.com",
    Port = 80,
    Credentials = new NetworkCredential("proxyuser", "password")})) {
        client.Host = "1.123.123.123";
        client.Port = 990;
        client.Credentials = new NetworkCredential("ftpuser", "password");
        client.SslProtocols = System.Security.Authentication.SslProtocols.Tls12;
        client.DataConnectionType = FtpDataConnectionType.EPSV;
        client.EncryptionMode = FtpEncryptionMode.Implicit;
        client.Connect();

        client.UploadFile(@"C:\test.csv", "/test.csv");
}

The comparison between FluentFTP log files and FileZilla Client log files shows the same operations.

FluentFTP log:

Command:  SIZE /test.csv
Response: 550 File not found

OpenWrite("/test.csv", Binary)
Command:  TYPE I
Response: 200 Type set to I

OpenPassiveDataStream(EPSV, "STOR /test.csv", 0)
Command:  EPSV
Response: 229 Entering Extended Passive Mode (|||40160|)
Status:   Connecting to 1.123.1.123:80 // HTTP-Proxy
HTTP/1.1 200 Connection established

Command:  STOR /test.csv
Response: 425 Can't open data connection for transfer of "/test.csv"
Status:   Disposing FtpSocketStream...

FileZilla client log:

Status: Starting upload of C:\test.csv
Command: CWD /
Response: 250 CWD successful. "/" is current directory.
Command: TYPE I
Response: 200 Type set to I
Command: EPSV
Response: 229 Entering Extended Passive Mode (|||40132|)
Command: STOR test.csv
Status: Connection with proxy established, performing handshake...
Response: Proxy reply: HTTP/1.1 200 Connection established
Response: 150 Opening data channel for file upload to server of "/test.csv"
Response: 226 Successfully transferred "/test.csv"
Status: File transfer successful, transferred 24 bytes in 1 second

Answer 1

I had the same problem and managed to upload the file with those settings:

ftpClient.SslProtocols = SslProtocols.None | SslProtocols.Tls12;
ftpClient.ValidateAnyCertificate = true;
ftpClient.DataConnectionEncryption = false;

I think the key here is DataConnectionEncryption.