web method problem

[lgriess]

I've posted this problem on several forums and no one has come up with the correct answer, but anyway here it goes:

I've tried stringifying and querystring'ing the parameter but the Response error continues to be
{"Message":"Object reference not set to an instance of an object.","StackTrace":" at ProvaReportLocale._Default.GetColumns() in \\ProvaReportLocale\\Default.aspx.cs:line 96","ExceptionType":"System.NullReferenceException"}

I have the following JSON call, the data I'm passing seems to be getting stringify'ed properly from what i'm looking at, however, I don't seem to have the right syntax to process the parameter in the public web method.

Here is the JSON call:

<script type="text/javascript" language="javascript"> 

  var qs = new Querystring();

  var v1 = qs.get("TorVName");

  var jsonData = JSON.stringify(v1);  

        $().ready(function() {
            $.ajax({
                type: "POST",
                url: "Default.aspx/GetColumns",
                data: jsonData,
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function(msg) {
       var optString = '<option value="-1">Select Column</option>';
        $.each(msg.d, function(index, item) {
        optString += '<option value="' + item + '">' + item + '</option>';
        });
        $('select[name^=DDLColumns]').html(optString);
                },
                error: function() {
                    alert("Failed to load columns");
                }
            });
        });
</script>

and here is the cooresponding web method:

[WebMethod]
    public static ArrayList GetColumns(string TorVName)
    {
        String cnstr = "myconnect string";
        string Sql = String.Empty;
        ArrayList arlist = new ArrayList();
        SqlDataReader rdr = null;
        SqlCommand cmd = null;
        DataSet dset;
        SqlConnection cn = new SqlConnection(cnstr);
        cn.Open();
        dset = new DataSet("ds");
        dset.Clear();

etc etc...

The whole thing works if I hard code the variable TorVName = "Whatever";
even passing back to the html page the ArrayList through json, so this is the last piece of the puzzle.

I have a hard time deciding how to debug a web method since I can only see the client side actions in firebug.

any help on how to recieve and process the parameter in the web method would be most appreciated.

Thanks Deano