What is wrong with my auto forum thread generator using HttpWebRequest?

I'm using HttpWebRequest to send request without using a brow开发者_高级运维ser but I always get this reply from this old school cgi forum: "duplicate thread". I'm pretty sure the thread is not a duplicate as it is the first time I send it. I'm guessing the forum software is detecting something unusual about my thread as is is machine generated. What can I do?

HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create("http://pop.6park.com/cgi-bin/know1/mainboard.pl");
myRequest.Method = "POST";
myRequest.ContentType = "application/x-www-form-urlencoded";
string postData = "name=ZhuangNan&usrpwd=aaa&subject=whatisthis&body=abcabcabcabc";
UTF8Encoding encoding = new UTF8Encoding();
byte[] byte1 = encoding.GetBytes(postData);
myRequest.ContentLength = byte1.Length;
Stream newStream = myRequest.GetRequestStream();
newStream.Write(byte1, 0, byte1.Length);

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If the target script tries to check the UserAgent HTTP header to determine if the request is being made by a browser, you can try populating the HttpWebRequest.UserAgent property with a valid value. This has worked for me on at least one occasion.

There are a number of other HTTP headers that you could set to make the target script think it is being hit by a browser rather than a program.

Check out any of the HTTP header properties that can be set. See HttpWebRequest Properties for more information.

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myRequest.ContentType = "application/x-www-form-urlencoded";
string postData = "name=ZhuangNan&usrpwd=aaa&subject=whatisthis&body=abcabcabcabc";

Not a MIME/baseenc data?