private bool doNotRecurseOnNote2 = false;

void BillingEngine_EinvNodeAdded(object sender, MercatorUi.Engine.Gescom.BillingEngine.EinvNodeAddedEventArgs e)
{
    MercatorUi.Engine.Gescom.BillingEngine billingEngine = (MercatorUi.Engine.Gescom.BillingEngine)sender;
    if ((e.Node.Name == "cbc:Note") && !doNotRecurseOnNote2 && (billingEngine.PIEDS["note2"].ToString().Trim() != string.Empty))
    {
        doNotRecurseOnNote2 = true;
        billingEngine.EinvAddNode(e.eInvoiceEnum, e.ParentNode, "cbc:Note", billingEngine.PIEDS["note2"].ToString().Trim());

        doNotRecurseOnNote2 = false;
    }
}