Its reversing order of attributes (XmlElements) set in Serializer
class.

namespace Windstream.Business
{
   [Serializable]
   public class Order
   {
       public Windstream.Business.Broadband Broadband;
       public Windstream.Business.POTS POTS;

       public Order()
       {
           // Default Constructor.
       }
// Order
       private string orderrequestid;

       public string OrderRequestId
       {
           get { return orderrequestid; }
           set { orderrequestid = value; }
       }

// CODE that instantiates Order, and calls XMLSerializer() .

Order _order = new Order();
_order.OrderRequestId = Session["OrderRequestId"].ToString();

_order.Broadband = new Broadband();
bbLineItem = new LineItem();
bbLineItem.ProductId =
int.Parse(hashBroadbandSpeed["ProductId"].ToString());
// ...
// ...
_order.Broadband.LineItems.LineItem = arrBBOrderItems;
bool bXml = XmlSerialize.ToXmlFile(_order);

public static class XmlSerialize
{

  public static bool ToXmlFile(Object objToXml)
       {
           // XmlTextWriter xtw = new XtmTextWriter();
           try
           {
               String _xmlFile;
               _xmlFile = XmlFilePath();
               StreamWriter strWriter = new StreamWriter(_xmlFile);
               XmlSerializer xmlSerializer = new
XmlSerializer(typeof(Windstream.Business.Order));
               xmlSerializer.Serialize(strWriter, objToXml);

}
}

OUTPUT:

<Order xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
 <Broadband>
   <LineItems>
     <LineItem>
       <Quantity />
       <ItemName>Broadband 6 Mbps</ItemName>
       <ProductId>112</ProductId>
       <Price>29.99</Price>
       <Description>Download Max. Speed of 6.0 Mbps, Upload Max Speed
of 384 Kbps. This pricing available for new customers only when
bundled with qualifying services.</Description>
       <FixedRecurringPrice>R</FixedRecurringPrice>
     </LineItem>
   </LineItems>
 </Broadband>
 <OrderRequestId>1</OrderRequestId>
</Order>