post form data

there is a poll form on the web that posts data to an ASP page
I created a html file localy and i am able to post form data just like this

<form name="frm" method="post" action="the url">
    <input type="hidden" name="voteChoice" value="498">
    <input type="hidden" name="PID" value="108">
    <input type="hidden" name="TID" value="7714">
    <input type="hidden" name="FID" value="33">
    <input type="hidden" name="PN" value="0">
    <input type="hidden" name="TPN" value="1">
    <input type="submit" name="Submit" value="Submit">
</form>

when I want to do this via java with the below code its not successfull to update the poll. i dont know why ?

import java.net.*;
import java.io.*;
import java.util.*;

public class PostForm {
    public static void main(String[] args) throws Exception {
        URL url = new URL("the url");
        String argString = "voteChoice=498&PID=108&TID=7714&FID=33&PN=0&TPN=1";
       
        argString = "voteChoice=498&PID=108&TID=7714&FID=33&PN=0&TPN=1";
       
        URLConnection con = url.openConnection();
        con.setDoInput(true);
        con.setDoOutput(true);
        con.setUseCaches(false);
        con.setRequestProperty("Referer", "http://www.google.com");
        con.setRequestProperty("User-Agent", "Mozilla/5.0");
        con.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
       
        // Write the arguments as post data
        OutputStream out = con.getOutputStream();
        out.write(argString.getBytes());
        out.flush();
        out.close();
       
        // Read the response
        InputStream is = con.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        String line = null;
        while((line = br.readLine()) != null) {
            System.out.println(line);
        }
        br.close();
    }
}