c # - file upload on ftp works only the first time

I have a function that sends files to an ftp, the first time I use it it works perfectly, however when I use it a second time it gets stuck on the line: using (Stream writer = ftpRequest.GetRequestStream ())

The full function code follows:

private void EnviarFTP(string CaminhoArquivoLocal, string CaminhoFTP, string NomeArquivoFTP)
{
    FtpWebRequest ftpRequest;
    FtpWebResponse ftpResponse;
    string sURI = "ftp://" + txtFTPServer.Text + "/" + CaminhoFTP;
    try
    {
        if (!CheckFileExistsFtp(sURI))
        {
            ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri(sURI));
            ftpRequest.Method = WebRequestMethods.Ftp.MakeDirectory;
            ftpRequest.Credentials = new NetworkCredential(txtFTPUser.Text, ftpPass);
            ftpRequest.UsePassive = true;
            ftpRequest.UseBinary = true;
            ftpRequest.KeepAlive = false;
            FtpWebResponse response = (FtpWebResponse)ftpRequest.GetResponse();
            Stream ftpStream = response.GetResponseStream();
            ftpStream.Close();
            response.Close();
        }

        ftpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri(sURI + NomeArquivoFTP));
        ftpRequest.Method = WebRequestMethods.Ftp.UploadFile;
        ftpRequest.Proxy = null;
        ftpRequest.UseBinary = true;
        ftpRequest.Credentials = new NetworkCredential(txtFTPUser.Text, ftpPass);
        ftpRequest.Timeout = 10000000;
        ftpRequest.ReadWriteTimeout = 10000000;

        //Seleção do arquivo a ser enviado
        FileInfo arquivo = new FileInfo(CaminhoArquivoLocal);
        byte[] fileContents = new byte[arquivo.Length];

        using (FileStream fr = arquivo.OpenRead())
        {
            fr.Read(fileContents, 0, Convert.ToInt32(arquivo.Length));
        }

        using (Stream writer = ftpRequest.GetRequestStream())
        {
            writer.Write(fileContents, 0, fileContents.Length);
        }

        //obtem o FtpWebResponse da operação de upload
        ftpResponse = (FtpWebResponse)ftpRequest.GetResponse();
        ftpResponse.Close();
        ftpRequest = null;
    }
    catch (WebException webex)
    {
        txtMsg.Text += Environment.NewLine + "ERRO=> " + webex.Message;
    }
}