When I clicked button, it initialize grid with multiheader columns and groupby features and then populate data to the grid by using web services. They looked so fine. I just clicked button again to do the same thing to get an error below

Uncaught Error: There was an error parsing the JSON data and applying the defined data schema: The input data doesn't match the schema, the following field couldn't be mapped: undefined

Below is Code

<script type="text/javascript" src="../../Components/IgniteUI/js/infragistics.lob.js"></script>

<script type="text/javascript">
$.ig.loader({
scriptPath: "../../Components/IgniteUI/js/",
cssPath: "../../Components/IgniteUI/css/",
resources: "igGrid.MultiColumnHeaders"
});
</script>

<script type="text/javascript">

var portfolioA = '';
var portfolioB = '';
var GetPortfolioCompareGrid = null;

Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);

function EndRequestHandler(sender, args) {
DataGrid();
};

$("[id$='btnCompare']").click(function (e) {
DataGrid();
e.preventDefault();
});

function DataGrid() {

var portfolioA = $find('<%=ddlportfolio.ClientID %>').get_selectedItem().get_value();
var portfolioB = $find('<%=ddlportfoliocompare.ClientID %>').get_selectedItem().get_value();

if (portfolioA != '' && portfolioB != '') {

$.ajax({
type: "POST",
url: "Modules/Portfolios/PortfolioWebService.asmx/GetPortfolioComparisonJSON",
data: "{portfolioA: '" + portfolioA + "',portfolioB:'" + portfolioB + "'}",
contentType: "application/json; charset=utf-8",
dataType: "json",
beforeSend: function () {
//$("#overlay").fadeIn();
},
success: function (response) {

var GetPortfolioCompareGrid = response.d;
debugger;
$("#ComparePortfolioTable").igGrid({
autoGenerateColumns: false,
columns:
[
{ headerText: "INVESTMENT NAME", key: "InvestmentTitle", dataType: "string", hidden: true },
{ headerText: "INVESTMENT ID", key: "InvestmentID", dataType: "string", hidden: true },
{ headerText: "UII", key: "UII", dataType: "string", hidden: true },
{ headerText: "Portfolio", key: "PortfolioName", dataType: "string" },
{ headerText: "Portfolio ID", key: "PortfolioID", dataType: "string", hidden: true },
{ headerText: "Template", key: "TemplateYear", dataType: "string" },
{ headerText: "PY-1 2013",
group: [
{ headerText: "DME", key: "PY2013DME", dataType: "number" },
{ headerText: "SS", key: "PY2013SS", dataType: "number" },
{ headerText: "Total", key: "PY2013Total", dataType: "number"}]
},
{ headerText: "PY 2014",
group: [
{ headerText: "DME", key: "PY2014DME", dataType: "number" },
{ headerText: "SS", key: "PY2014SS", dataType: "number" },
{ headerText: "Total", key: "PY2014Total", dataType: "number"}]
},
{ headerText: "CY 2015",
group: [
{ headerText: "DME", key: "CY2015DME", dataType: "number" },
{ headerText: "SS", key: "CY2015SS", dataType: "number" },
{ headerText: "Total", key: "CY2015Total", dataType: "number" }
]
},
{ headerText: "BY 2016",
group: [
{ headerText: "DME", key: "BY2016DME", dataType: "number" },
{ headerText: "SS", key: "BY2016SS", dataType: "number" },
{ headerText: "Total", key: "BY2016Total", dataType: "number" }
]
},
{ headerText: "BY+1 2017",
group: [
{ headerText: "DME", key: "BY2017DME", dataType: "number" },
{ headerText: "SS", key: "BY2017SS", dataType: "number" },
{ headerText: "Total", key: "BY2017Total", dataType: "number" }
]
}
],
width: "100%",
height: "500px",
dataSource: GetPortfolioCompareGrid,
dataSourceType: "json",
features:
[
{
name: 'GroupBy',
groupByAreaVisibility: 'hidden',
type: 'local',
columnSettings:
[
{ columnKey: "InvestmentTitle", isGroupBy: true }
]
},
{
name: 'MultiColumnHeaders'
}
]
//localSchemaTransform: true

}); //End igGrid Function
}, //end success
error: function (response) {
console.log(response);
},
complete: function () {
//$("#overlay").fadeOut();
}
}); //end ajax function

}

}

</script>