title: A potentially dangerous Request.Form value was detected from the client (
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/81991/a-potentially-dangerous-request-form-value-was-detected-from-the-client">A potentially dangerous Request.Form value was detected from the client</a>  </p>
  </blockquote>
  
  
  
  <p>I got error messages:<br></p>
  
  <pre><code> A potentially dangerous Request.Form value was detected from the client 
   (ctl00$MainContent$textboxError=...
  </code></pre>
  
  <p><br>after I run asp.net (C#) web application. how can I fix it?  </p>
  
  <p>Here is my code.</p>
  
  <pre><code>using System;
  using System.Data;
  using System.Configuration;
  using System.Web; 
  using System.Web.Security;
  using System.Web.UI;
  using System.Web.UI.WebControls;
  using System.Web.UI.HtmlControls;
  using System.Net;
  using System.Text.RegularExpressions;
  
  namespace SMS
  {
  public partial class _Default : System.Web.UI.Page
  {
  protected void Page_Load(object sender, EventArgs e)
  {
      textboxRecipient.Width = 400;
      textboxMessage.Width = 450;
      textboxMessage.Rows = 10;
      textboxError.Width = 400;
      textboxError.Rows = 5;
  
      textboxError.ForeColor = System.Drawing.Color.Red;
      textboxError.Visible = false;
      textboxError.Text = "";
  
      if (!Page.IsPostBack)
      {
          textboxRecipient.Text = "+85593840396";
          textboxMessage.Text = "Hello World!";
      }
  }
  protected void buttonSendOnClick(object sender, EventArgs e)
  {
  
      if (textboxRecipient.Text == "")
      {
          textboxError.Text += "Recipient(s) field must not be empty!\n";
          textboxError.Visible = true;
          return;
      }
  
  
      string ozSURL = "http://127.0.0.1"; //where Ozeki NG SMS Gateway is running
      string ozSPort = "9501"; //port number where Ozeki NG SMS Gateway is listening
      string ozUser = HttpUtility.UrlEncode("tenh"); //username for successful login
      string ozPassw = HttpUtility.UrlEncode("tenh123"); //user's password
      string ozMessageType = "SMS:TEXT"; //type of message
      string ozRecipients = HttpUtility.UrlEncode(textboxRecipient.Text); 
      string ozMessageData = HttpUtility.UrlEncode(textboxMessage.Text); 
  
      string createdURL = ozSURL + ":" + ozSPort + "/httpapi" +
          "?action=sendMessage" +
          "&amp;username=" + ozUser +
          "&amp;password=" + ozPassw +
          "&amp;messageType=" + ozMessageType +
          "&amp;recipient=" + ozRecipients +
          "&amp;messageData=" + ozMessageData;
  
      try
      {
  
          HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create(createdURL);
  
  
          HttpWebResponse myResp = (HttpWebResponse)myReq.GetResponse();
          System.IO.StreamReader respStreamReader=new 
  
        System.IO.StreamReader(myResp.GetResponseStream());
          string responseString = respStreamReader.ReadToEnd();
          respStreamReader.Close();
          myResp.Close();
  
          //inform the user
          textboxError.Text = responseString;
          textboxError.Visible = true;
      }
      catch (Exception)
      {
  
          textboxError.Text = "Ozeki NG SMS Gateway Server is not running!";
          textboxError.Visible = true;
      }
  
    }
    }
    }
  </code></pre>
  
  <p>I already add codes below to my web.config :</p>
  
  <pre><code>   validateRequest="false" and requestValidationMode="2.0"
  </code></pre>