L'analyse JSON avec JSON.NET

J'ai une chaîne JSON:

 {"responseData": 
{"results": [
{"GsearchResultClass": "GblogSearch",
"title":"\u003cb\u003eParis Hilton\u003c/b\u003e shops at Sydney Michelle boutique in the Beverly Glen \u003cb\u003e...\u003c/b\u003e",
"titleNoFormatting":"Paris Hilton shops at Sydney Michelle boutique in the Beverly Glen ...",
"postUrl":"http://www.celebrity-gossip.net/celebrities/hollywood/paris-hilton-sydney-michelle-stockup-215844/",
"content":"\u003cb\u003eParis Hilton\u003c/b\u003e shops at Sydney Michelle boutique in the Beverly Glen Mall - \u003cb\u003eParis Hilton\u003c/b\u003e: Sydney Michelle Stockup.",
"author":"The Gossip Girls at (c) gossipgirls.com",
"blogUrl":"http://www.celebrity-gossip.net/",
"publishedDate":"Tue, 23 Feb 2010 22:26:00 -0800"
},
{"GsearchResultClass":"GblogSearch",
"title":"\u003cb\u003eParis Hilton\u003c/b\u003e having wardrobe woes as she met with her lawyer",
"titleNoFormatting":"Paris Hilton having wardrobe woes as she met with her lawyer",
"postUrl":"http://www.celebrity-gossip.net/celebrities/hollywood/paris-hiltons-wardrobe-woes-215855/",
"content":"\u003cb\u003eParis Hilton\u003c/b\u003e having wardrobe woes as  she met with her lawyer - \u003cb\u003eParis Hilton's\u003c/b\u003e Wardrobe Woes.",
"author":"The Gossip Girls at (c) gossipgirls.com","blogUrl":"http://www.celebrity-gossip.net/",
"publishedDate":"Wed, 24 Feb 2010 11:07:56 -0800"
},
{"GsearchResultClass":"GblogSearch",
"title":"HOT GALLERY: \u003cb\u003eParis Hilton\u003c/b\u003e Turns Her Frown Upside Down | OK \u003cb\u003e...\u003c/b\u003e",
"titleNoFormatting":"HOT GALLERY: Paris Hilton Turns Her Frown Upside Down | OK ...",
"postUrl":"http://www.okmagazine.com/2010/02/hot-gallery-paris-hilton-turns-her-frown-upside-down/",
"content":"\u003cb\u003eParis Hilton\u003c/b\u003e kept her game face on yesterday as she headed to a meeting in Hollywood. The socialite maintained her composure, but eventually cracked a smile, 201002.",
"author":"Brittany Talarico",
"blogUrl":"http://www.okmagazine.com/",
"publishedDate":"Wed, 24 Feb 2010 07:57:10 -0800"
},
{"GsearchResultClass":"GblogSearch",
"title":"Love It Or Hate It: \u003cb\u003eParis Hilton\u003c/b\u003e | ImNotObsessed.com",
"titleNoFormatting":"Love It Or Hate It: Paris Hilton | ImNotObsessed.com",
"postUrl":"http://www.imnotobsessed.com/2010/02/24/love-it-or-hate-it-paris-hilton",
"content":"tweetmeme_url \u003d \"http://www.imnotobsessed.com/2010/02/24/love-it-or-hate-it-\u003cb\u003eparis\u003c/b\u003e-\u003cb\u003ehilton\u003c/b\u003e\";tweetmeme_element_id \u003d '#tweetmeme-widget-139430e62dc37d7a2aa71840d6444572';That's some dress \u003cb\u003eParis Hilton\u003c/b\u003e was seen wearing while shopping in ...",
"author":"Vera",
"blogUrl":"http://www.imnotobsessed.com/",
"publishedDate":"Wed, 24 Feb 2010 10:44:28 -0800"
}],
"cursor": { 
"pages": [
{"start":"0","label":1},
{"start":"4","label":2},
{"start":"8","label":3},
{"start":"12","label":4},
{"start":"16","label":5},
{"start":"20","label":6},
{"start":"24","label":7},
{"start":"28","label":8}],
"estimatedResultCount":"8035445",
"currentPageIndex":0,
"moreResultsUrl":"http://blogsearch.google.com/blogsearch?oe\u003dutf8\u0026ie\u003dutf8\u0026safe\u003dactive\u0026source\u003duds\u0026start\u003d0\u0026hl\u003den\u0026q\u003dParis+Hilton"
}
}, 
"responseDetails": null, 
"responseStatus": 200}

ed. remarque: les sauts de ligne ajouté pour des raisons de lisibilité

et je suis en utilisant Json.NET pour l'analyser, mais sa me donne une valeur null

c'est mon code:

JObject o = JObject.Parse(json); //<- where json is the string above
string name = (string)o["responseData"];

MAIS sa me donne cette erreur :

Ne peut pas convertir {null} à la Chaîne. 
InformationsquelleAutor C.. | 2010-02-25