Services: Getting error 406 Node type is required - but I have specified the node type I'm trying to create a node using jQuery to POST JSON.

I get the following error returned by the server:
Failed to load resource: the server responded with a status of 406 (Not Acceptable: Node type is required)

However, the type is definitely specified in my JSON string:

var data = '{"title":"Sample post ",
  "type":"article",
  "field_link":
            [{
             "url":"http://www.google.com", 
            "title":"My title"
            }],
  "body":
            {
             "und":[{"value":"comments about something"}]
             }
  }';
try to observe the order of fields like: type > title > body > fields
that is the widget type of "field_link"?
add "und" to this field

{"title":"Sample post ",
"type":"article",
"body":{
"und":[{
"value":"comments about something"}]},
"field_link":{
"und":[{
"url":"http://www.google.com",
"title":"My title"}]}}