JSON - pass param?

I guess I am still doing something wrong...

my jquery:

$(document).ready(function ()
{
    var loc = window.location.href;

    if (loc.indexOf("CreateNewUser") != -1)
    {
        // alert("check if user name avail");

        $.ajax({
            type: "POST",
            url: "WebGlobalMethods.asmx/NameIsAvailable",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            data: { "newusername": "max" },
            success: function (msg)
            {
                alert("success");
            },
            error: function (msg)
            {
                alert("failed:  " + msg.d);

            }
        });
    }
});

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my web method (web service call):

  [WebMethod]
        public bool NameIsAvailable(string newusername)
        {
            bool nameavail = false;

            if (newusername != "")
            {
                connectToDB myDB = new connectToDB();
                object myObject = new
                {
                    LOGIN = newusername
                };
                string strPickDataReturn = myDB.getStringResult(1, "IWEB.CHECK.USERNAME", myObject);

                XmlDocument doc = new XmlDocument();
                string test = strPickDataReturn;

                doc.LoadXml(strPickDataReturn);

                System.Data.DataSet tmpDS = new DataSet();
                System.IO.StringReader stream;
                stream = new System.IO.StringReader(doc.InnerXml);
                tmpDS.ReadXml(stream);

                if (tmpDS.Tables[0].TableName == "ERRORS")
                {
                    nameavail = false;
                }
                else
                {
                    nameavail = true;
                }
            }

            return nameavail;
        }//end of web method

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In my jquery, this part is getting called:

  error: function (msg)
            {
                alert("failed:  " + msg.d);

            }


The message that appears at runtime is

failed : undefined


Is there a way to make the message more verbose?

I needed single quotes around the data:

wrong:   data: { "newusername" : "max" },

correct:   data: '{ "newusername" : "max" }',

$(document).ready(function ()
{
    var loc = window.location.href;

    if (loc.indexOf("CreateNewUser") != -1)
    {
        // alert("check if user name avail");

        var msg;

        $.ajax({
            type: "POST",
            url: "WebGlobalMethods.asmx/NameIsAvailable",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            data: '{ "newusername" : "max" }',
            success: function (msg)
            {
                alert("success");
            },
            error: function (msg)
            {
                alert("failed:  " + msg.d);

            }
        });
    }
});

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thx!