How to fix "Length of the data to decrypt is invalid" in this code

Question

I have some troubles with the code below. It's not my own, i copied it from this question on Stack Overflow.

public readonly byte[] salt = new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; // Must be at least eight bytes.  MAKE THIS SALTIER!
public const int iterations = 1042; // Recommendation is >= 1000.       


/// <summary>Decrypt a file.</summary>
/// <remarks>NB: "Padding is invalid and cannot be removed." is the Universal CryptoServices error.  Make sure the password, salt and iterations are correct before getting nervous.</remarks>
/// <param name="sourceFilename">The full path and name of the file to be decrypted.</param>
/// <param name="destinationFilename">The full path and name of the file to be output.</param>
/// <param name="password">The password for the decryption.</param>
/// <param name="salt">The salt to be applied to the password.</param>
/// <param name="iterations">The number of iterations Rfc2898DeriveBytes should use before generating the key and initialization vector for the decryption.</param>
public void DecryptFile(string sourceFilename, string destinationFilename, string password, byte[] salt, int iterations)
{
    AesManaged aes = new AesManaged();
    aes.BlockSize = aes.LegalBlockSizes[0].MaxSize;
    aes.KeySize = aes.LegalKeySizes[0].MaxSize;
    // NB: Rfc2898DeriveBytes initialization and subsequent calls to   GetBytes   must be eactly the same, including order, on both the encryption and decryption sides.
    Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(password, salt, iterations);
    aes.Key = key.GetBytes(aes.KeySize / 8);
    aes.IV = key.GetBytes(aes.BlockSize / 8);
    aes.Mode = CipherMode.CBC;
    ICryptoTransform transform = aes.CreateDecryptor(aes.Key, aes.IV);

    using (FileStream destination = new FileStream(destinationFilename, FileMode.CreateNew, FileAccess.Write, FileShare.None))
    {
        using (CryptoStream cryptoStream = new CryptoStream(destination, transform, CryptoStreamMode.Write))
        {
            try
            {
                using (FileStream source = new FileStream(sourceFilename, FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    source.CopyTo(cryptoStream);
                    source.Flush();
                }
            }
            catch (CryptographicException exception)
            {
                if (exception.Message == "Padding is invalid and cannot be removed.")
                    throw new ApplicationException("Universal Microsoft Cryptographic Exception (Not to be believed!)", exception);
                else
                    throw;
            }
        }
    }
}

/// <summary>Encrypt a file.</summary>
/// <param name="sourceFilename">The full path and name of the file to be encrypted.</param>
/// <param name="destinationFilename">The full path and name of the file to be output.</param>
/// <param name="password">The password for the encryption.</param>
/// <param name="salt">The salt to be applied to the password.</param>
/// <param name="iterations">The number of iterations Rfc2898DeriveBytes should use before generating the key and initialization vector for the decryption.</param>
public void EncryptFile(string sourceFilename, string destinationFilename, string password, byte[] salt, int iterations)
{
    AesManaged aes = new AesManaged();
    aes.BlockSize = aes.LegalBlockSizes[0].MaxSize;
    aes.KeySize = aes.LegalKeySizes[0].MaxSize;
    // NB: Rfc2898DeriveBytes initialization and subsequent calls to   GetBytes   must be eactly the same, including order, on both the encryption and decryption sides.
    Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(password, salt, iterations);
    aes.Key = key.GetBytes(aes.KeySize / 8);
    aes.IV = key.GetBytes(aes.BlockSize / 8);
    aes.Mode = CipherMode.CBC;
    ICryptoTransform transform = aes.CreateEncryptor(aes.Key, aes.IV);

    using (FileStream destination = new FileStream(destinationFilename, FileMode.CreateNew, FileAccess.Write, FileShare.None))
    {
        using (CryptoStream cryptoStream = new CryptoStream(destination, transform, CryptoStreamMode.Write))
        {
            using (FileStream source = new FileStream(sourceFilename, FileMode.Open, FileAccess.Read, FileShare.Read))
            {
                source.CopyTo(cryptoStream);
            }
        }
    }
}

After that I got an exception: Length of data to decrypt is invalid. But after that file, which I encrypted, is encrypted anyway, but when you try to decrypt this, it shows the message: Not enough memory to finish this operation. Anyway, it works correctly with multimedia files (I tried .mp3, .mkv, .jpg), but not correctly with documents (.txt, .docx). So, I hope that somebody can help me with it, and another one question (its for this theme). How to save password for every file? Every time, when you use an incorrect password to decrypt a file, it doesn't decrypt it. Is there a way to show that the password is incorrect?