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

when the data is posted to http://www.zhubajie.com/task/user/register?it 
fails without any error msg 
my code : 
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        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&e mail=cydhdfdsu...@cyhfucku.com&passregtext=1&uFrom=no ...