I ran into a very similar problem with my Xamarin Windows Phone 8.1 app. The reason JObject.Parse(json) would not work for me was because my Json had a beginning "[" and an ending "]". In order to make it work, I had to remove those two characters. From your example, it looks like you might have the same issue.
jsonResult = jsonResult.TrimStart(new char[] { '[' }).TrimEnd(new char[] { ']' });
I was then able to use the JObject.Parse(jsonResult) and everything worked.