Javascript error alert message fired before call to NewStatement is complete

Question

I have the following Javascript code contained on the click event of an upload button where I want to record an xAPI statement. I have put a breakpoint on my Admin/NewStatement method and although it is hitting it the page is always displaying the error message even before I have stepped through the breakpoint. Why is this failing all the time?

var postData = {
  'userID': 1,
  'verbID': 26,
  'objectID':1
};

$.ajax({
  type: "GET",
  cache: false,
  dataType: "json",
  url: "/Admin/NewStatement",
  data: postData,
  success: function (data) {
    var json = data;
    alert("THIS IS MY JSON" + json);
    //tincan.sendStatement(json);
  },
  error: function (error) {
    alert("An Error has occurred during the Creation of this xAPI Statement");
    alert(error);                
  }
});

I have the following method at Admin/NewStatement

public string NewStatement(int userID, int verbID, int objectID)
    { 
        string result;
        result = avm.AddStatement(userID, verbID, objectID);
        return result;
    }

avm.AddStatement refers to my ViewModel code:

public string AddStatement(int userID, int verbID, int objectID)
    {
        Actor actor = actorRepository.Get(a => a.UserID == userID).FirstOrDefault();
        Verb verb = verbRepository.Get(v => v.VerbID == verbID).FirstOrDefault();
        StatementObject statementObject = statementObjectRepository.Get(o => o.StatementObjectID == objectID).FirstOrDefault();

        Statement newStatement = new Statement();
        newStatement.id = System.Guid.NewGuid();
        newStatement.ActorID = actor.ActorID;
        newStatement.VerbID = verb.VerbID;
        newStatement.StatementObjectID = statementObject.StatementObjectID;

        this.statementRepository.Add(newStatement);
        this.statementRepository.SaveChanges();

        JsonSerializerSettings jss = new JsonSerializerSettings();
        jss.ObjectCreationHandling = ObjectCreationHandling.Auto;
        var json = JsonConvert.SerializeObject(newStatement);
        return json.ToString();
    }