Query string module encryption not working properly

#region Using
using System;
using System.IO;
using System.Web;
using System.Text;
using System.Security.Cryptography;

#endregion

/// <summary>
/// Summary description for QueryStringModule
/// </summary>
public class QueryStringModule : IHttpModule
{

#region IHttpModule Members

public void Dispose()
{
    // Nothing to dispose
}

public void Init(HttpApplication context)
{
    context.BeginRequest += new EventHandler(context_BeginRequest);
}

#endregion

private const string PARAMETER_NAME = "enc=";
private const string ENCRYPTION_KEY = "key";

void context_BeginRequest(object sender, EventArgs e)
{
    HttpContext context = HttpContext.Current;
    if (context.Request.Url.OriginalString.Contains("aspx") && context.Request.RawUrl.Contains("?"))
    {
        string query = ExtractQuery(context.Request.RawUrl);
        string path = GetVirtualPath();

        if (query.StartsWith(PARAMETER_NAME, StringComparison.OrdinalIgnoreCase))
        {
            // Decrypts the query string and rewrites the path.
            string rawQuery = query.Replace(PARAMETER_NAME, string.Empty);
            string decryptedQuery = Decrypt(rawQuery);
            context.RewritePath(path, string.Empty, decryptedQuery);
        }
        else if (context.Request.HttpMethod == "GET")
        {
            // Encrypt the query string and redirects to the encrypted URL.
            // Remove if you don't want all query strings to be encrypted automatically.
            string encryptedQuery = Encrypt(query);
            context.Response.Redirect(path + encryptedQuery);
        }
    }
}

/// <summary>
/// Parses the current URL and extracts the virtual path without query string.
/// </summary>
/// <returns>The virtual path of the current URL.</returns>
private static string GetVirtualPath()
{
    string path = HttpContext.Current.Request.RawUrl;
    path = path.Substring(0, path.IndexOf("?"));
    path = path.Substring(path.LastIndexOf("/") + 1);
    return path;
}

/// <summary>
/// Parses a URL and returns the query string.
/// </summary>
/// <param name="url">The URL to parse.</param>
/// <returns>The query string without the question mark.</returns>
private static string ExtractQuery(string url)
{
    int index = url.IndexOf("?") + 1;
    return url.Substring(index);
}

#region Encryption/decryption

/// <summary>
/// The salt value used to strengthen the encryption.
/// </summary>
private readonly static byte[] SALT = Encoding.ASCII.GetBytes(ENCRYPTION_KEY.Length.ToString());

/// <summary>
/// Encrypts any string using the Rijndael algorithm.
/// </summary>
/// <param name="inputText">The string to encrypt.</param>
/// <returns>A Base64 encrypted string.</returns>
public static string Encrypt(string inputText)
{
    RijndaelManaged rijndaelCipher = new RijndaelManaged();
    byte[] plainText = Encoding.Unicode.GetBytes(inputText);
    PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(ENCRYPTION_KEY, SALT);

    using (ICryptoTransform encryptor = rijndaelCipher.CreateEncryptor(SecretKey.GetBytes(32), SecretKey.GetBytes(16)))
    {
        using (MemoryStream memoryStream = new MemoryStream())
        {
            using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
            {
                cryptoStream.Write(plainText, 0, plainText.Length);
                cryptoStream.FlushFinalBlock();
                return "?" + PARAMETER_NAME + Convert.ToBase64String(memoryStream.ToArray());
            }
        }
    }
}

/// <summary>
/// Decrypts a previously encrypted string.
/// </summary>
/// <param name="inputText">The encrypted string to decrypt.</param>
/// <returns>A decrypted string.</returns>
public static string Decrypt(string inputText)
{
    RijndaelManaged rijndaelCipher = new RijndaelManaged();
    byte[] encryptedData = Convert.FromBase64String(inputText);
    PasswordDeriveBytes secretKey = new PasswordDeriveBytes(ENCRYPTION_KEY, SALT);

    using (ICryptoTransform decryptor = rijndaelCipher.CreateDecryptor(secretKey.GetBytes(32), secretKey.GetBytes(16)))
    {
        using (MemoryStream memoryStream = new MemoryStream(encryptedData))
        {
            using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
            {
                byte[] plainText = new byte[encryptedData.Length];
                int decryptedCount = cryptoStream.Read(plainText, 0, plainText.Length);
                return Encoding.Unicode.GetString(plainText, 0, decryptedCount);
            }
        }
    }
}

#endregion

}

protected void Button1_Click(object sender, EventArgs e)
{
   string sONbr = sONbrTextBox.Text;
   string SOLine = sOLineTextBox.Text;
   string SerialNbr = serialNbrTextBox.Text;
   string PalletID = palletIDTextBox.Text;
   string PackingListNo = PackingListNoTextBox.Text;
   string StatusCode = statusCodeComboBox.Text;
   string PackType = packTypeComboBox.Text;
   string CrUserID = Request.QueryString["LogInUser"].ToString();

   if (string.IsNullOrWhiteSpace(sONbr) || string.IsNullOrWhiteSpace(SOLine) || string.IsNullOrWhiteSpace(PalletID) || string.IsNullOrWhiteSpace(PackingListNo) || string.IsNullOrWhiteSpace(StatusCode) || string.IsNullOrWhiteSpace(PackType))
   {
      status_lbl.Text = "Please fill in all the information.";
      status_lbl.Visible = true;
      GridView1.Visible = false;
      return;
   }
   else if (string.IsNullOrWhiteSpace(CrUserID))
   {
      status_lbl.Text = "Please login your account!";
      status_lbl.Visible = true;
      ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Please login your account!')</script>");
      Response.Redirect("Login Page.aspx");
      GridView1.Visible = false;
      return;
   }
   else
   {
      SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["constr_TESTINGSystem"].ToString());
      conn.Open();

      SqlCommand comm = conn.CreateCommand();
      comm.CommandType = CommandType.StoredProcedure;
      comm.CommandText = "usp_TagNumberUpdate";

      comm.Parameters.AddWithValue("@sONbr", sONbr);
      comm.Parameters.AddWithValue("@SOLine", SOLine);
      comm.Parameters.AddWithValue("@SerialNbr", SerialNbr);
      comm.Parameters.AddWithValue("@PalletID", PalletID);
      comm.Parameters.AddWithValue("@PackingListNo", PackingListNo);
      comm.Parameters.AddWithValue("@StatusCode", StatusCode);
      comm.Parameters.AddWithValue("@PackType", PackType);
      comm.Parameters.AddWithValue("@CrUserID", CrUserID);

      SqlParameter ReturnVal = comm.Parameters.Add("@return", SqlDbType.NVarChar,200);
      ReturnVal.Direction = ParameterDirection.Output;

      comm.ExecuteNonQuery();

      string val = (string)ReturnVal.Value;

      conn.Close();
      status_lbl.Text = val;
      status_lbl.Visible = true;
      CheckBox1.Checked = false;
      serialNbrTextBox.ReadOnly = true;
      serialNbrTextBox.BackColor = System.Drawing.ColorTranslator.FromHtml("#A9A9A9");
      serialNbrTextBox.Text = "N/A";
      sONbrTextBox.Text = sOLineTextBox.Text = palletIDTextBox.Text = PackingListNoTextBox.Text = "";
      GridView1.Visible = false;
   }
}

protected void Button2_Click(object sender, EventArgs e)
{
   string sONbr = sONbrTextBox.Text;
   string SOLine = sOLineTextBox.Text;
   string SerialNbr = serialNbrTextBox.Text;

   if (string.IsNullOrWhiteSpace(sONbr) || string.IsNullOrWhiteSpace(SOLine) || string.IsNullOrWhiteSpace(SerialNbr))
   {
      status_lbl.Text = "Please fill in SO #, SO LINE & SERIAL NO to check record.";
      status_lbl.Visible = true;
      GridView1.Visible = false;
      return;
   }
   else
   {
      status_lbl.Text = "Inquiry Successful!";
      status_lbl.Visible = true;
      GridView1.Visible = true;
   }
}