$.ajax({
    type: "GET",
    url: "Home/LogIn",
    data: { userName: username, password: password },
    dataType: 'json',
    succes: function (data) {
        alert(data.d + '  Succes')
    },
    failure: function (data) {
        alert(data.d + '  failure');
    }
});

public string LogIn(string userName, string password)
{
    LogInController loginController = (LogInController)Session["LogInController"];

    User tempuser = loginController.CheckLogin(password, userName);

    if (tempuser != null)
    {
        massdrop = new MassdropShop(tempuser);
        Session["LoggedInName"] = tempuser.Name;
        Session["massdrop"] = massdrop;
        return "1";
    }
    else
        return "0";
}

succes: function (data) {
        alert(data.d + '  Succes')
    },

success: function (data) {
        alert(data.d + '  Succes')
    },

data:{ userName: username, password: password },

change
data:JSON.stringify{ userName: username, password: password },
success: function (data) {


            alert(JSON.stringify(data.d));