SSH host key fingerprint "ssh-rsa 2048 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx" does not mat

try
{
    // Setup session options
    SessionOptions sessionOptions = new SessionOptions
    {
        Protocol = Protocol.Sftp,
        HostName = ftpServer,
        UserName = ftpUser,
        Password = ftpPassword,
        //GiveUpSecurityAndAcceptAnySshHostKey = false,
        SshHostKeyFingerprint = "ssh-rsa 2048 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx",
        SshPrivateKeyPath = PrivateKeyFile,
        PortNumber = 22,
        SshPrivateKeyPassphrase = PrivateKeyPass
    };
/////Here I get the exception?/// Why?
 
    using (Session session = new Session())
    {
        session.Open(sessionOptions);
 
        // Upload files
        TransferOptions transferOptions = new TransferOptions();
        transferOptions.TransferMode = TransferMode.Binary;
 
        TransferOperationResult transferResult;
        transferResult = session.PutFiles(localfilename, ftpfilename, false, transferOptions);
        transferResult.Check(); 
        if (transferResult.IsSuccess)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}
catch (Exception e)
{
    writeToLog(true, e.Message.ToString());
    throw new Exception(e.Message);
}