The XML data must have the same schema as the CustomFieldDataSet. Try reading a custom field into a CustomFieldDataSet, and then use
WriteXml to write out the XML to a file, to see the schema (or use the
WriteXmlSchema method). For a code example, see the ReadCustomFieldsByMdPropUids2 method in the SDK.
Also, you'd probably want to use the ReadXml method on the DataTable to import one or more rows of data into a
CustomFieldsDataTable within the CustomFieldDataSet.
--Jim
Jim Corbin [MSFT]