logging into other website programatically in c# only working for some websites

logging into other website programatically in c# only working for some
websites

this code have taken from stackoverflow itself this code only works for
one website http://www.e3mel.com/login.aspx when i check the same code for
other urls such as https://www.grouprevmax.com/WebMARDSV2/Login.aspx it
does not work.Here is the code please check if had done anything wrong
string url = "http://www.e3mel.com/login.aspx";//
HttpContext.Current.Request.Url.AbsoluteUri.ToString().Replace("AutoLogin",
"Login");
CookieContainer myCookieContainer = new CookieContainer();
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
request.CookieContainer = myCookieContainer;
request.Method = "GET";
request.KeepAlive = false;
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
System.IO.Stream responseStream = response.GetResponseStream();
System.IO.StreamReader reader = new
System.IO.StreamReader(responseStream, Encoding.UTF8);
string srcString = reader.ReadToEnd();
// get the page ViewState
string viewStateFlag = "id=\"__VIEWSTATE\" value=\"";
int i = srcString.IndexOf(viewStateFlag) + viewStateFlag.Length;
int j = srcString.IndexOf("\"", i);
string viewState = srcString.Substring(i, j - i);
// get page EventValidation
string eventValidationFlag = "id=\"__EVENTVALIDATION\" value=\"";
i = srcString.IndexOf(eventValidationFlag) + eventValidationFlag.Length;
j = srcString.IndexOf("\"", i);
string eventValidation = srcString.Substring(i, j - i);
string submitButton = "LoginButton";
// UserName and Password
string userName = "xxxxx";
string password = "xxxxx";
// Convert the text into the url encoding string
viewState = System.Web.HttpUtility.UrlEncode(viewState);
eventValidation = System.Web.HttpUtility.UrlEncode(eventValidation);
submitButton = System.Web.HttpUtility.UrlEncode(submitButton);
// Concat the string data which will be submit
string formatString =
"email_id={0}&pass_word={1}&btnlogin={2}&__VIEWSTATE={3}&__EVENTVALIDATION={4}";
string postString =
string.Format(formatString, userName, password, submitButton,
viewState, eventValidation);
// Convert the submit string data into the byte array
byte[] postData = Encoding.ASCII.GetBytes(postString);
// Set the request parameters
request = WebRequest.Create(url) as HttpWebRequest;
request.Method = "POST";
request.Referer = url;
request.KeepAlive = false;
request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT
6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR
3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2;
CIBA)";
request.ContentType = "application/x-www-form-urlencoded";
request.CookieContainer = myCookieContainer;
System.Net.Cookie ck = new System.Net.Cookie("TestCookie1", "Value of
test cookie");
ck.Domain = request.RequestUri.Host;
request.CookieContainer.Add(ck);
request.CookieContainer.Add(response.Cookies);
request.ContentLength = postData.Length;
// Submit the request data
System.IO.Stream outputStream = request.GetRequestStream();
request.AllowAutoRedirect = true;
outputStream.Write(postData, 0, postData.Length);
outputStream.Close();
// Get the return data
response = request.GetResponse() as HttpWebResponse;
responseStream = response.GetResponseStream();
reader = new System.IO.StreamReader(responseStream, Encoding.UTF8);
srcString = reader.ReadToEnd();
Response.Write(srcString);
Response.End();