Adding System.Net reference into .Net Protocol script

I am trying to create a script in .net protocol taking reference of code below. But am getting a reference error 

//---------------------------------------------
//Script Title        :
//Script Description  :
//
//
//Recorder Version    : 
//---------------------------------------------
using System.Net;  
using System.IO;  
using System.Text;  

namespace Script
{
    public partial class VuserClass
    {
        public int Action()
        {
        	
        	        // Get the object used to communicate with the server.  
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://www.contoso.com/test.htm");  
            request.Method = WebRequestMethods.Ftp.UploadFile;  
  
            // This example assumes the FTP site uses anonymous logon.  
            request.Credentials = new NetworkCredential ("anonymous","janeDoe@contoso.com");  
  
            // Copy the contents of the file to the request stream.  
            StreamReader sourceStream = new StreamReader("testfile.txt");  
            byte [] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd());  
            sourceStream.Close();  
            request.ContentLength = fileContents.Length;  
  
            Stream requestStream = request.GetRequestStream();  
            requestStream.Write(fileContents, 0, fileContents.Length);  
            requestStream.Close();  
  
            FtpWebResponse response = (FtpWebResponse)request.GetResponse();  
  
            Console.WriteLine("Upload File Complete, status {0}", response.StatusDescription);  
  
            response.Close();  
            
            return 0;
        }
    }
}

Error: 

Error 8 The type or namespace name 'Net' does not exist in the namespace 'System' (are you missing an assembly reference?) Action.cs   DotNet1