Need help with this source code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Security.Cryptography;

namespace EncryptionDecryption
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            DesObj = Rijndael.Create();
        }

        string NormalString;
        byte[] CipherBytes;
        byte[] PlainBytes;
        byte[] PlainBytes2;
        byte[] PlainKey;
        SymmetricAlgorithm DesObj;

        private void btnEncrypt_Click(object sender, EventArgs e)
        {
            NormalString = txtboxNormalString.Text;
            PlainBytes = Encoding.ASCII.GetBytes(NormalString);
            PlainKey = Encoding.ASCII.GetBytes("12845726gh3846gs");
            DesObj.Key = PlainKey;
            DesObj.Mode = CipherMode.CBC;
            DesObj.Padding = PaddingMode.PKCS7;
            System****.MemoryStream ms = new System****.MemoryStream();
            CryptoStream cs = new CryptoStream(ms,DesObj.CreateEncryptor(), CryptoStreamMode.Write);
            cs.Write(PlainBytes, 0, PlainBytes.Length);
            cs.Close();
            CipherBytes = ms.ToArray();
            ms.Close();
            txtboxEncryptedString.Text = Encoding.ASCII.GetString(CipherBytes);
        }

        private void btnDecrypt_Click(object sender, EventArgs e)
        {
            System****.MemoryStream ms1 = new System****.MemoryStream(CipherBytes);
            CryptoStream cs1 = new CryptoStream(ms1, DesObj.CreateDecryptor(), CryptoStreamMode.Read);
            cs1.Read(CipherBytes, 0, CipherBytes.Length);
            PlainBytes2 = ms1.ToArray();
            cs1.Close();
            ms1.Close();
            txtboxDecryptedString.Text = Encoding.ASCII.GetString(PlainBytes2);
        }