Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.List`1
To make it clear, in addition to @SLaks' answer, that meant you need to change this line :
List<RootObject> datalist = JsonConvert.DeserializeObject<List<RootObject>>(jsonstring);
to something like this :
RootObject datalist = JsonConvert.DeserializeObject<RootObject>(jsonstring);
As the error message is trying very hard to tell you, you can't deserialize a single object into a collection (List<>).
You want to deserialize into a single RootObject.