var jsonData = [];

    populateGrid();// Here is ajax call, jsonData array is populated

    var g23=$('#ipCC').combogrid({
        panelWidth: 450,
        value: '006',
        idField: 'customerID',
        textField: 'fullName',
        source:jsonData,//JSON.parse(jsonData),
        columns: [[
                {field: 'customerID', title: 'customerID', width: 60 },
                {field: 'fullName', title: 'fullName', width: 100 }
            ]]
    });

    var g25 = $('#ipCC').combogrid('grid');//<-----------------error
    g25.datagrid('loadData', jsonData);