JDOM how to insert Element:HELP!!!

[dottbin]

hi all,
I created following code:

Namespace xmlns = Namespace.getNamespace("configData.xsd");
            Namespace xn = Namespace.getNamespace("xn","genericNrm.xsd");
            Namespace un = Namespace.getNamespace("un","utranNrm.xsd");
            Namespace gn = Namespace.getNamespace("gn","geranNrm.xsd");
            Namespace es = Namespace.getNamespace("es","SpecificAttributes.10.22");
            Namespace xsi = Namespace.getNamespace("xsi","http://www.w3.org/2001/XMLSchema-instance");
           
            Element root = new Element("bulkCmConfigDataFile");
             //insert namespace
            root.setNamespace(Namespace.getNamespace( "configData.xsd" ));
            root.addNamespaceDeclaration(xn);
            root.addNamespaceDeclaration(un);
            root.addNamespaceDeclaration(gn);
            root.addNamespaceDeclaration(es);
            root.addNamespaceDeclaration(xsi);

root.addContent(new Element("fileHeader",Namespace.getNamespace( "configData.xsd" )).setAttribute("fileFormatVersion", "32.615 V4.5").setAttribute("vendorName", "VENDOR")
        .addContent(new Element("configData",Namespace.getNamespace( "configData.xsd" )).
            addContent(new Element("SubNetwork",xn).setAttribute("id", "Italia_R").
                addContent(new Element("userDefinedNetworkType",xn).addContent("UTRAN")).
                addContent(new Element("SubNetwork",xn).setAttribute("id", "NAERNC0236")))));

List<Element> a = new ArrayList<Element>();
ElementFilter eFilter = new ElementFilter("SubNetwork", xn);

Iterator elementList=root.getDescendants(eFilter);

while (elementList.hasNext()) {
    System.out.print(elementList.hasNext());
Element nextElement = (Element) elementList.next();
System.out.print(nextElement);
a.add(nextElement);
        }
for (Element el : a){
    el.addContent(new Element("hello",es));
    
}

XMLOutputter outputter = new XMLOutputter();
outputter.setFormat((outputter.getFormat().getPrettyFormat()));

I would like to insert child Element("hello",es) when Element("SubNetwork",xn) is found on Element root.
But Java generates following error:

java.util.ConcurrentModificationException

How can I solve this issue?

Thx in advanced

[dottbin]

My code works fine :D
I forgot to delete a command line :p