Apache httpclient + ntlm Authentication

I have a client to upload a file to the server through the https post. It uses a proxy server and this is my code

public void upload() throws Exception {

    //create default client
    DefaultHttpClient client = new DefaultHttpClient();

    //set proxy authentication if specified
    if (proxy.equals("yes") && proxyAuth.equals("yes")){
    client.getCredentialsProvider().setCredentials(
            new AuthScope(address, port),
            new UsernamePasswordCredentials(proxyUsername, proxyPassword));
    }

    //set proxy if specified
    if (proxy.equals("yes")){
        HttpHost proxy = new HttpHost(address, port);
        client.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY,proxy);
    }

    HttpPost post = new HttpPost(url);
    MultipartEntity entity = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE);

    File dir = new File(inputFilePath);
    File[] fileArray = dir.listFiles(); 
    File file = fileArray[0];

    FileBody uploadFilePart = new FileBody(file);

    entity.addPart("file", uploadFilePart);
    entity.addPart("username", new StringBody(username));
    entity.addPart("password", new StringBody(password));

    post.setEntity(entity);

    //execute post and get response
    String response = EntityUtils.toString(client.execute(post).getEntity(), "UTF-8");

    client.getConnectionManager().shutdown();

    log4j.info(response);

    if(!response.substring(0, 3).equalsIgnoreCase("200")){
        Exception e = new Exception("An error has occurred server side: ");
        throw e;
    }
}

Now the problem is that it works fine sometimes, and sometimes I get the following error.

org.apache.http.impl.client.AbstractAuthenticationHandler.selectScheme (AbstractAuthenticationHandler.java:149) - ntlm authentication scheme is not supported "