What is wrong in my XML structure to add nodes using a RESTFul web service POST?
After a lot of research about my question I've changed to json format, which works fine.

I still think I have an error in my XML structure, but since it works with JSON now, I switched to using that instead.  

UPDATE: With this json data it works fine.

{ "title":"Test page", 
  "type":"page", 
  "status":0, 
  "language":"es", 
  "author":1,
  "body":{  "value": "Aptent bene capto euismod ...",
            "summary":"", 
            "format":"filtered_html"
         }
}