Jquery Ajax Posting JSON to webservice

You mentioned using json2.js to stringify your data, but the POSTed data appears to be URLEncoded JSON You may have already seen it, but this post about the invalid JSON primitive covers why the JSON is being URLEncoded.

I'd advise against passing a raw, manually-serialized JSON string into your method. ASP.NET is going to automatically JSON deserialize the request's POST data, so if you're manually serializing and sending a JSON string to ASP.NET, you'll actually end up having to JSON serialize your JSON serialized string.

I'd suggest something more along these lines:

var markers = [{ "position": "128.3657142857143", "markerPosition": "7" },
               { "position": "235.1944023323615", "markerPosition": "19" },
               { "position": "42.5978231292517", "markerPosition": "-3" }];

$.ajax({
    type: "POST",
    url: "/webservices/PodcastService.asmx/CreateMarkers",
    // The key needs to match your method's input parameter (case-sensitive).
    data: JSON.stringify({ Markers: markers }),
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function(data){alert(data);},
    error: function(errMsg) {
        alert(errMsg);
    }
});

The key to avoiding the invalid JSON primitive issue is to pass jQuery a JSON string for the data parameter, not a JavaScript object, so that jQuery doesn't attempt to URLEncode your data.

On the server-side, match your method's input parameters to the shape of the data you're passing in:

public class Marker
{
  public decimal position { get; set; }
  public int markerPosition { get; set; }
}

[WebMethod]
public string CreateMarkers(List<Marker> Markers)
{
  return "Received " + Markers.Count + " markers.";
}

You can also accept an array, like Marker[] Markers, if you prefer. The deserializer that ASMX ScriptServices uses (JavaScriptSerializer) is pretty flexible, and will do what it can to convert your input data into the server-side type you specify.

1. markers is not a JSON object. It is a normal JavaScript object.
2. Read about the data: option:

   Data to be sent to the server. It is converted to a query string, if not already a string.

If you want to send the data as JSON, you have to encode it first:

data: {markers: JSON.stringify(markers)}

jQuery does not convert objects or arrays to JSON automatically.

But I assume the error message comes from interpreting the response of the service. The text you send back is not JSON. JSON strings have to be enclosed in double quotes. So you'd have to do:

return "\"received markers\"";

I'm not sure if your actual problem is sending or receiving the data.