Hashtable docProps = new Hashtable();
docProps.Add("Field1", myvalue);
docProps.Add("Field2", "slsl");
docProps.Add("Field3", "wwowowo");
try
{
DocumentSet ds = DocumentSet.Create(list.RootFolder, "mydocumentset", list.ContentTypes["CustomDocumentSet"].Id, docProps);
}
This will add the document set, but value of the hashtalbe is not being accepted.