Problem with XML DOM, writing in XML document

Hi!
I have a problem with writing to an XML file. When i run my program, the c# give me an exception: "The node to be inserted is from a different document context.". I looked a bit on the exception and I found the answers , that this is happening when we write from one document to another. But i dont write from one to another, but I write from the object to xml file. This is the code where the program shows me exception:

private XmlDocument novDokument = new XmlDocument();

public void zapisiArtikleKiSoNaZalogiVnewDoc(string vhodna, string izhodna)
{
    int i = 1;

    newDoc.AppendChild(newDoc.CreateXmlDeclaration(new Version(1, 0).ToString(), Encoding.UTF8.BodyName, string.Empty));
    XmlElement novSeznamArtikel = newDoc.CreateElement("seznamArtiklov");

    foreach (Artikel a in seznamPrebranihArtiklov)
    {
        if (Convert.ToInt16(a.zalogaA) > 0)
        {
            XmlElement novArtikel = newDoc.CreateElement("artikel");
            novArtikel.SetAttribute("id", i.ToString());

            XmlElement novNaziv = newDoc.CreateElement("naziv");
            novNaziv.InnerText = a.nazivA;
            novArtikel.AppendChild(novNaziv);

            XmlElement novaCena = newDoc.CreateElement("cena");
            novaCena.InnerText = a.cenaA;
            novArtikel.AppendChild(novaCena);


            XmlElement novDatum = newDoc.CreateElement("datum");
            novArtikel.AppendChild(novDatum);

            XmlElement novNabave = doc.CreateElement("nabave");
            novNabave.InnerText = a.datumNabaveA;
            novDatum.AppendChild(novNabave); //HERE RAISES AN EXCEPTION

            novSeznamArtikel.AppendChild(novArtikel);
            i++;
        }
    }

    newDoc.AppendChild(novSeznamArtikel);

    XmlTextWriter tw = new XmlTextWriter(izhodna, null);
    tw.Formatting = Formatting.Indented;
    newDoc.WriteContentTo(tw);

    tw.Close();
}

And XML document should look like this:

<?xml version="1.0" encoding="utf-8" ?>
<seznamArtiklov>
  <artikel id="1">
    <naziv>Kruh</naziv>
    <cena>3</cena>
    <datum>
      <nabave>03.09.2012</nabave>
    </datum>
  </artikel>
</seznamArtiklov

If anyone knows the solution to my problem is very welcome. To answer thank you in advance!

Tags: C#, XML, DOM