Android Upload image in string to c #

I'm sending images from Android to the server in C # but when I try to do the conversion it makes an error in this conversion.

In android I make this conversion:

ByteArrayOutputStream stream = new ByteArrayOutputStream();

bitmapPhoto.compress(Bitmap.CompressFormat.JPEG, 50, stream);
final byte[] img_byte = stream.toByteArray();

final String imageString = Base64.encodeToString(img_byte, Base64.DEFAULT);

On the c # server I get the string and re-convert to image:

byte[] novaFoto = Convert.FromBase64String(NovaFoto.FotoString);

using (MemoryStream stream = new MemoryStream(novaFoto))
{
    Image image = Image.FromStream(stream);
}

Sometimes it makes an error converting to byte [] and sometimes gives error in Image.FromStream

Can anyone help me with this?