How to update/add customer using web service proxy for Vantage 8.0

I am trying to build a mobile solution (i.e. web portal to access the
Vantage Service 8.0.3 via web service
adapter calls).

I am trying to update the customers by using the following
code:

System.IO.Stream streamInMemory = new System.IO.MemoryStream();
XmlSerializer s = new XmlSerializer(typeof
(Epicor.Mfg.BO.CustomerDataSet));
s.Serialize(streamInMemory, customerDataSet);

reader = XmlReader.Create(streamInMemory);
reader.MoveToContent(); //Move to the cd element node.

XmlDocument xDoc = new XmlDocument();
XmlNode xNode = xDoc.ReadNode(reader);

returnVal = customerAdapter.ExecuteMethod("Update", new object
[] { xNode });

where the customerDataSet is the new CustomerDataSet that I want
to update.

The code does NOT throw exception to me, but the returnVal[0] is
always null without any explaination. Of course, the customerDataSet
does not get updated.

Do any of you have had the similar experience? What is the correct
way to update a DataSet via Vantage webservice calls.

Thanks,

-- Charlie