Using fnServerData to get JSON from an asmx web service

I am having trouble getting the fnServerData to poplulate the DataTable. My web service is called fine and returning data that I can access, however the DataTable constantly says "Processing"

I have it working fine with this code which gets the returned JSON from the web service before calling the dataTable plugin, however I need to be able to use the ServerSide processing as well for large datasets which I am assuming will not work with this method for obvious reasons.

Working code:

    $.ajax({
        type: "POST",
        url: "http://localhost:52350/Webservice/AllReports.asmx/GetAllReports",
        data: "{}",
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (json) {
            //alert(json.d);
            //alert(json.d[0].SDRRID);
            //alert(json.d[0].ReportNumber);
            $('#example').dataTable({
                "bProcessing": true,
                "bJQueryUI": true,
                "sPaginationType": "full_numbers",
                "aaData": json.d,
                "aoColumns": [
			       { "mDataProp": "SDRRID" },
			       { "mDataProp": "ReportNumber" }
                 ]
            });
        }
    });

Non-working code:

    $('#example').dataTable({
        "bProcessing": true,
      //  "bServerSide": true,
        "sAjaxSource": 'http://localhost:52350/Webservice/AllReports.asmx/GetAllReports',
        "aoColumns": [
            { "mDataProp": "SDRRID" },
            { "mDataProp": "ReportNumber" }
        ],
        "fnServerData": function (sSource, aoData, fnCallback, oSettings) {
            oSettings.jqXHR = $.ajax({
                "dataType": 'json',
                "contentType": "application/json; charset=utf-8",
                "type": "POST",
                "url": sSource,
                "data": aoData,
                "success": function (json) {
                //    alert(json.d);
                //    alert(json.d[0].SDRRID);
                //    alert(json.d[0].ReportNumber);
                    fnCallback(json.d);
                }
            });
        }
        });

If I uncomment my alerts I get actual data so I know the web service is being called and returned correctly. I do have to deal with .d from the asmx web service, but it seems to work fine in the first example so I am not sure why it won't work fine in the second example.

Thanks!

Tim