succeed in across-domain posting from site a to site b usingwebclient,but one fail..

[dotnet]

when the data is posted to http://www.zhubajie.com/task/user/register，it
fails without any error msg
my code :
WebClient webClient = new WebClient();
webClient.Headers.Add("Content-Type", "application/x-www-form-
urlencoded");
byte[] postData = Encoding.ASCII.GetBytes
("username=ccccccgfcccccc&password=cccckjcccccds&repassword=cccckjcccccds&[email protected]&passregtext=1&uFrom=no&forward=&url=&welcome=");
byte[] responseData = webClient.UploadData("http://
www.zhubajie.com/task/user/regnex", "POST", postData);
string pageHtml = Encoding.UTF8.GetString(responseData);
Response.Write(pageHtml);