I try to use the UltraWebTab in my application, but I’m getting an error “Microsoft JScript runtime error: 'this._postBackSettings.async' is null or not an object” when I change between tabs.

Please help me how to avoid this error

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="AssortmentDashBoard.aspx.cs"

    Inherits="AssortmentTools_AssortmentDashBoard" Title=":.Hendry Assortment Tools.: Assortment Tools"

    MasterPageFile="~/MasterPages/Hendry.master" %>

<asp:Content ID="AssortmentContent" ContentPlaceHolderID="BodyPlaceHolder" runat="server">

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

 function CollapseLeftNav()

    {

        collapse();

    }

    </script>

            <igtab:UltraWebTab ID="tabsAssortment" runat="server" EnableViewState="true" AutoPostBack="true" Height="680px" Width="99%"

                BarHeight="0" BorderWidth="0" OnTabClick="tabsAssortment_TabClick" >

                <DefaultTabStyle Height="20px" ForeColor="white" Font-Bold="true" />

                <RoundedImage FillStyle="LeftMergedWithCenter" HoverImage="../images/tab_hover.gif"

                    NormalImage="../images/tab_top_normal.gif" SelectedImage="../images/tab.gif" />

                <HoverTabStyle ForeColor="black">

                </HoverTabStyle>

                <Tabs>

                    <igtab:Tab Key="Recommend Assortment" Text="Recommend Assortment">

                    </igtab:Tab>

                    <igtab:Tab Key ="Compare Assortment" Text="Compare Assortment">

                    </igtab:Tab>

                    <igtab:Tab Key="Examine Assortment" Text="Examine Assortment">

                    </igtab:Tab>

                    <igtab:Tab Key="Share Scenarios" Text="Share Scenarios">

                    </igtab:Tab>

                </Tabs>

            </igtab:UltraWebTab>

</asp:Content>

And the code behind is as below.

public partial class AssortmentTools_AssortmentDashBoard : System.Web.UI.Page

{

    protected void Page_Load(object sender, EventArgs e)

    {

        ((MasterPages_Hendry)this.Page.Master).PageTitle = "Assortment Tools Dashboard";

        ((MasterPages_Hendry)this.Page.Master).AddBodyAttribute("onload", "CollapseLeftNav()");

        if (Session["AddProduct"] != null)

        {

            tabsAssortment.SelectedTabIndex = 1;

        }

        else

        {

            tabsAssortment.SelectedTabIndex = 0;

        }

    }

    protected void tabsAssortment_TabClick(object sender, Infragistics.WebUI.UltraWebTab.WebTabEvent e)

    {

        if (e.Tab.Key.ToString() == "Compare Assortment")

        {

            e.Tab.ContentPane.TargetUrl = "../AssortmentTools/CompareAssortment.aspx";

            tabsAssortment.DataBind();

            tabsAssortment.SelectedTabIndex = 1;

         }

    }

    protected override void OnInit(EventArgs e)

    {

        InitializeComponent();

        base.OnInit(e);

    }

    private void InitializeComponent()

    {

    }

}