Serialize dataset:

                   MemoryStream stream = new MemoryStream();
                   dataset.WriteXml(stream, XmlWriteMode.DiffGram );
                   stream.Seek(0, SeekOrigin.Begin);
                   StreamReader sr = new StreamReader(stream);
                   datasetstring = sr.ReadToEnd();
                 
this is the datastring:

“<diffgr:diffgram xmlns:msdata=\"urn:schemas-microsoft-com:xml-msdata\"
xmlns:diffgr=\"urn:schemas-microsoft-com:xml-diffgram-v1\">\r\n  
<NewDataSet>\r\n    <Table1 diffgr:id=\"Table11\" msdata:rowOrder=\"0\"
diffgr:hasChanges=\"modified\">\r\n      <ID>1</ID>\r\n      
<NUMMER>1001</NUMMER>\r\n      <ACHTERNAAM>Changed</ACHTERNAAM>\r\n    
</Table1>\r\n  </NewDataSet>\r\n  <diffgr:before>\r\n    <Table1
diffgr:id=\"Table11\" msdata:rowOrder=\"0\">\r\n      <ID>1</ID>\r\n      
<NUMMER>1001</NUMMER>\r\n      <ACHTERNAAM>BlaBla</ACHTERNAAM>\r\n    
</Table1>\r\n  </diffgr:before>\r\n</diffgr:diffgram>"

Now deserialize:
//--deserialize
                   StringReader stringReader = new
StringReader(datasetstring);
                   DataSet ds = new DataSet();
                   ds.ReadXml(stringReader,XmlReadMode.DiffGram );

Now dataset ds is empty, what am I doing wrong ?
I use VS2008