RadComboBox used within ModalPopupExtender - Unable to populate data

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Hi,

I have used telerik: RadCombobox with ModelPopupExtender in my application.
I am unable to populate data.
Refer code block to suggest solution.
Kindly Suggest on urgent basis.
Thanks in advance.

<cc1:ModalPopupExtender ID="pop_email"  runat="server" TargetControlID="btn_EmailReport" PopupControlID="pan_email" OkControlID="btn_email_Send" CancelControlID="btn_email_cancel"/>
<asp:Panel ID="pan_email" runat="server"  CssClass="PopUpControl_Pannel" Style="display: none">
<asp:UpdatePanel ID="up_email" runat="server" UpdateMode="Conditional">
                                <ContentTemplate>
                                    <asp:Table ID="tbl_email" runat="server">

                                        <asp:TableRow>

                                            <asp:TableCell Width="10px">
                                               <telerik:RadComboBox ID="RadCmbBox_email_to" runat="server"
                                                    DataTextField="company" DataValueField="email"
                                                    AllowCustomText="true" EmptyMessage="" ZIndex="100000999" ShowDropDownOnTextboxClick="true">
                                             <ItemTemplate>
                                                        <div>
                                                              <asp:Label ID="lbl_emailID1" runat="server" Text="Alapattah" />
                                                               <asp:Label ID="lbl_emailID2" runat="server" Text="Brickell Avenue" />
                                                               <asp:Label ID="lbl_emailID3" runat="server" Text="Downtown Miami" />
                                                        </div>
                                                    </ItemTemplate>
                                                </telerik:RadComboBox>

                                            </asp:TableCell>
                                        </asp:TableRow>
                                    </asp:Table>
                               </ContentTemplate>
                            </asp:UpdatePanel>
                        </asp:Panel>