Devexpress combobox used in update panel

HI,
I am create one web application, In which i am use devexpress component and ajax toolkit control. i am use update panel and in this update panel i am use devexpress combobox. and i am fire SelectedIndexChanged of this combobox.
but when i am run the application combobox fill from database but they give the error like Microsoft JScript runtime error: 'parentNode' is null or not an object
ASPX page

<asp:UpdatePanel ID="UpdatePanelAddInfo" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true">
<ContentTemplate>
                                    <table align="center">
                                        <tr>
                                            <td colspan="2">
                                                <asp:Label ID="Label8" runat="server" ForeColor="Red" CssClass="text_red"></asp:Label>
                                            </td>
                                        </tr>
                                        <tr>
                                            <td align="left">
                                                <asp:Label ID="lblItemTitle" runat="server" Text="Title*:" CssClass="text"></asp:Label>
                                            </td>
                                            <td align="left">
                                                <asp:TextBox ID="txtTitle" runat="server" Width="250px" OnFocus="this.style.borderColor='#666699'"
                                                    OnBlur="this.style.borderColor=''" CssClass="TextBoxInPanel" TabIndex="1"></asp:TextBox>
                                                <br />
                                            </td>
                                        </tr>
                                        <tr>
                                            <td align="left">
                                                <asp:Label ID="lblAuthor" runat="server" CssClass="text" Text="Author:"></asp:Label>
                                            </td>
                                            <td align="left">
                                                <%--  <asp:DropDownList ID="ddlAuthor" runat="server" CssClass="ComboBox1">
                                                    </asp:DropDownList>--%>
                                               
                                                <dx:aspxcombobox id="ddlAuthor" runat="server" CssClass="ComboBox1" 
                                                    dropdownstyle="DropDown" incrementalfilteringmode="StartsWith"
                                                    autopostback="true" enablecallbackmode="True" 
                                                    onselectedindexchanged="ddlAuthor_SelectedIndexChanged" 
                                                    oncallback="ddlAuthor_Callback" >
                                                    </dx:aspxcombobox>
                                            </td>
                                        </tr>
</table>
                                </ContentTemplate>
                            </asp:UpdatePanel>

.cs

protected void ddlAuthor_SelectedIndexChanged(object sender, EventArgs e)
    {
       

        try
        {
            if (ddlAuthor.Text != "")
            {
                string CheckValue = ddlAuthor.SelectedIndex.ToString();

                if (CheckValue == "-1")
                {
                    ModalPopupExtenderDisplayMsg.Show();
                    ScriptManager.RegisterClientScriptBlock(UpdatePanelAddInfo, this.GetType(), "Script1", "AsyncMessenger();", true);
                }
            }
            else
            {
                ModalPopupExtenderDisplayMsg.Hide();
                ScriptManager.RegisterClientScriptBlock(UpdatePanelAddInfo, this.GetType(), "Script1", "AsyncMessenger();", true);
            }
        }
        catch (Exception)
        {
        }
    }
    protected void ddlAuthor_Callback(object sender, DevExpress.Web.ASPxClasses.CallbackEventArgsBase e)
    {
        ddlAuthor.DataBind();
    }