Could not successfully simulate the form login using c# programming code - httpwebrequest

Question

Currently I'm trying to simulate the Login using c# code (HttpWebRequest/HttpWebResponse), however I ended up with the login.aspx webpage's html text rather than the html text after successful login.
the returned variable 'html' is exactly the same with the login.aspx webpage itself, seems it did not post the data at all. please help. thank you. dave. here is the code i used
var LOGIN_URL = "http://altech.com.au/login.aspx";
HttpWebRequest webRequest = WebRequest.Create(LOGIN_URL) as HttpWebRequest;
StreamReader responseReader = new StreamReader(
webRequest.GetResponse().GetResponseStream());
string responseData = responseReader.ReadToEnd();
responseReader.Close();
string postData =String.Format(
"ctl00$ContentPlaceHolderBodyMain$txtEmail {0}&ctl00$ContentPlaceHolderBodyMain$txtPassword={1}&btnLogin=Login","myemail", "mypassword");
//have a cookie container ready to receive the forms auth cookie
CookieContainer cookies = new CookieContainer();
// now post to the login form
webRequest = WebRequest.Create(LOGIN_URL) as HttpWebRequest;
webRequest.Method = "POST";
webRequest.ContentType = "application/x-www-form-urlencoded";
webRequest.CookieContainer = cookies;
webRequest.UserAgent = "Mozilla/5.0 (Windows NT 5.2; WOW64; rv:2.0.1) Gecko/20100101 Firefox/4.0.1";
// write the form values into the request message
StreamWriter requestWriter = new StreamWriter(webRequest.GetRequestStream());
requestWriter.Write(postData);
requestWriter.Close();
HttpWebResponse response2 = (HttpWebResponse)webRequest.GetResponse();
StreamReader sr2 = new StreamReader(response2.GetResponseStream(), Encoding.Default);
string html = sr2.ReadToEnd();

Answer 1

You need to URL encode your data or it will not be accepted.
Dictionary<string, string> FormData = new Dictionary<string, string>();
//Add all of your name/value pairs to the dictionary
FormData.Add(
"ctl00$ScriptManager1",
"ctl00$ContentPlaceHolderBodyMain...");
...then to format it correctly...
public string GetUrlEncodedPostData(
Dictionary<string, string> FormData)
{
StringBuilder builder = new StringBuilder();
for (int i = 0; i < FormData.Count(); ++i)
{
//Better to use string.join, but this is a bit more clear ^_^
builder.AppendFormat(
"{0}={1}&",
WebUtility.UrlEncode(InputNameValue.ElementAt(i).Key),
WebUtility.UrlEncode(InputNameValue.ElementAt(i).Value));
}
//Remove trailing &
builder.Remove(builder.Length - 1, 1);
return builder.ToString();
}