wp7 - POST http request with parameters in request body using RestSharp - windows-phone-7

Question

I am trying to POST parameters through the request, to a service that returns a JSON object. The service works well for android and iOS. I am trying to get this working for wp7. The service requires the content type to be 'application/json' I have pasted the code that sets up the http request below:
var client = new RestClient(baseurl);
var request = new RestRequest();
request.Resource = "login";
request.Method = Method.POST;
request.AddHeader("Accept", "application/json");
request.AddHeader("content-type", "application/json");
request.RequestFormat = DataFormat.Json;
var postData = new Dictionary<string, string>()
{
{"key1",value1},
{"key2",value2}
};
request.AddBody(postData);
client.ExecuteAsync(request, response =>
{
var jsonUser = response.Content;
});
The response error I get from the server is an internal server error. Is anything wrong with the code above. I also tried request.AddParameter method but ended with the same result. The code for that is below:
var client = new RestClient(baseurl);
var request = new RestRequest();
request.Resource = "login";
request.Method = Method.POST;
request.AddHeader("Accept", "application/json");
request.AddHeader("content-type", "application/json");
request.RequestFormat = DataFormat.Json;
var postData = new Dictionary<string, string>()
{
{"key1",value1},
{"key2",value2}
};
var json = JsonConvert.SerializeObject(postData);
request.AddParameter("application/json", json, ParameterType.RequestBody);
client.ExecuteAsync(request, response =>
{
var jsonUser = response.Content;
});
Is there anything that I am doing wrong in either of the cases?