Compact Framework - get error in line 'webRequest.GetRequestStream()'

i'm new in mobile platform, i already find many related post for many days. i using Microsoft Visual Studio 2008, language is C#,
hope experts in forum can help me find the solution, thank you.

the code is work fine in desktop application but when move to compact
framework, some error found,one of the error show below:

below is my code

HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
webRequest.Method = "POST";
webRequest.Timeout = 12000;
webRequest.ContentType = "application/x-www-form-urlencoded";
webRequest.KeepAlive = false;

Byte[] bytes = Encoding.GetEncoding("UTF-8").GetBytes(this.Param);
Stream os = null;
WebResponse webResponse = null;
HttpWebResponse response = null;
StreamReader sr = null;
String errorMsg = "-999-" + System.Environment.NewLine;

try
{
webRequest.ContentLength = bytes.Length;
//i get the error 'System.Net.ProtocolViolationException' in this line
os = webRequest.GetRequestStream();
os.Write(bytes, 0, bytes.Length);
webResponse = webRequest.GetResponse();
sr = new StreamReader(webResponse.GetResponseStream(), System.Text.Encoding.
GetEncoding("UTF-8"));
this.Value = sr.ReadToEnd().Trim();
}

hope the following screenshot can make you more understand what problem i facing:

http://www.freeimagehosting.net/

when run in desktop application, the item inside webRequest without (!)
infront, but when move to mobile application, many item have (!) infront, i
tried to set webRequest.accept= null, but not work.
Please help.....

after i do more testing, i found that the symbol come out after i select "upgrade project" i think HttpWebRequest not support for all platform.

after i downgrade to 2.0, i get another error, i found that StringSplitOptions is not supported, have anyone can point me a correct direction how to fix this error, thank you