showing error Padding is invalid and cannot be removed.

string Salt = "Kosher", HashAlgorithm = "SHA1";

            int PasswordIterations = 2;
            string InitialVector = "OFRna73m*aze01xY";

            int KeySize = 256;
            if (string.IsNullOrEmpty(CipherText))
                return "";
            byte[] InitialVectorBytes = System.Text.Encoding.ASCII.GetBytes(InitialVector);
            byte[] SaltValueBytes = System.Text.Encoding.ASCII.GetBytes(Salt);

            byte[] CipherTextBytes = Convert.FromBase64String(CipherText);
            PasswordDeriveBytes DerivedPassword = new PasswordDeriveBytes(Password, SaltValueBytes, HashAlgorithm, PasswordIterations);
            byte[] KeyBytes = DerivedPassword.GetBytes(KeySize / 8);
            RijndaelManaged SymmetricKey = new RijndaelManaged();
            SymmetricKey.Mode = CipherMode.CBC;
            byte[] PlainTextBytes = new byte[CipherTextBytes.Length];
            int ByteCount = 0;
            using (ICryptoTransform Decryptor = SymmetricKey.CreateDecryptor(KeyBytes, InitialVectorBytes))
            {
                using (MemoryStream MemStream = new MemoryStream(CipherTextBytes))
                {
                    using (CryptoStream CryptoStream = new CryptoStream(MemStream, Decryptor, CryptoStreamMode.Read))
                    {

                        ByteCount = CryptoStream.Read(PlainTextBytes, 0, PlainTextBytes.Length);
                        MemStream.Close();
                        CryptoStream.Close();
                    }
                }
            }
            SymmetricKey.Clear();
            return System.Text.Encoding.UTF8.GetString(PlainTextBytes, 0, ByteCount);

 ByteCount = CryptoStream.Read(PlainTextBytes, 0, PlainTextBytes.Length) this line as  <br />
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Padding is invalid and cannot be removed<br />
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Any body know why error like this arising?<br />
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Thanks in Advance