Get or Set Xmlfield values

Hi,

I'm trying to get an xmlfield value, set with a smartform. In the workspace, I see my xmlfield value is ok :

- <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
- <User>
  <Name>toto4</Name> 
  <Address>toto4@toto</Address> 
  </User>

  </xs:schema>

But with this code (generate with the data manipulation event), I have an error :

.Value = TargetField;
  K2.Synchronous = true;
}

And the error is :

System.Exception: XPath : "Root/User/Name" could not be resolved on this document.
   at SourceCode.K2Utilities.XmlFieldHelper.XMLValueInternal(XmlDocument poXMLDoc, String psXPath, Object pValue, String psMethod)
   at SourceCode.K2Utilities.XMLFieldMod.GetXMLValue(String xml, String XPath)
   at K2Code1850.Main(ServerEventContext& K2)

I don't understand what's wrong ...
In my XmlField miss the root element.
I built this xmlfield in a smartform like that :

.Value = doc.OuterXml; 
pi.Update();

connexion.Close();

Thx

Aude