Padding is invalid and cannot be removed

Question

Hi I try to write simple code about encryption-decryption some text.
It encrypts well but after decryption it throws en exception "Padding is invalid and cannot be removed" during stream reader reads.That line is : "textBox1.text = sr.ReadToEnd();"

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            FileStream fs = new FileStream(@"C:\enkripcija.txt", FileMode.Open, FileAccess.ReadWrite);
           RijndaelManaged rm = new RijndaelManaged();

        
            CryptoStream cs = new CryptoStream(fs, rm.CreateEncryptor(rm.Key, rm.IV), CryptoStreamMode.Write);
          
            StreamWriter sw = new StreamWriter(cs, Encoding.UTF8);
            sw.Write("Something written for encryption");
            sw.Close();
            cs.Close();
            fs.Close();

        }

        private void button2_Click(object sender, EventArgs e)
        {
            FileStream fs = new FileStream(@"C:\enkripcija.txt", FileMode.Open, FileAccess.Read);
            RijndaelManaged rm = new RijndaelManaged();

        
            CryptoStream cs = new CryptoStream(fs, rm.CreateDecryptor(rm.Key, rm.IV), CryptoStreamMode.Read);
            StreamReader sr = new StreamReader(cs, Encoding.UTF8);

            textBox1.text = sr.ReadToEnd();
         
            sr.Close();
            cs.Close();
            fs.Close();
        }

      

      
    }