ถอดรหัสข้อความด้วย des แต่ขึ้น bad data แก้ไขยังไงครับ

Dim myDESProvider As DESCryptoServiceProvider = New DESCryptoServiceProvider()

        myDESProvider.Key = ASCIIEncoding.ASCII.GetBytes(Me.KeyPass)
        myDESProvider.IV = ASCIIEncoding.ASCII.GetBytes(Me.KeyPass)

        Dim DecryptedFile As FileStream = New FileStream("c:\scib\data.txt", FileMode.Open, FileAccess.Read)
        Dim myICryptoTransform As ICryptoTransform = myDESProvider.CreateDecryptor(myDESProvider.Key, myDESProvider.IV)
        Dim myCryptoStream As CryptoStream = New CryptoStream(DecryptedFile, myICryptoTransform, CryptoStreamMode.Read)

        Dim myDecStreamReader As New StreamReader(myCryptoStream, System.Text.Encoding.Default)
        Dim myDecStreamWriter As New StreamWriter("c:\scib\ok.txt", False, System.Text.Encoding.Default)

        myDecStreamWriter.Write(myDecStreamReader.ReadToEnd())

        myCryptoStream.Close()
        myDecStreamReader.Close()
        myDecStreamWriter.Close()