Ajax problem

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Ajax

I have used Ajax in my page to load the data from the server side.

I have a combobox filled with data, when selected it should send the selected item to server and get the data to fill in the second combobox.

When the item in the second combobox is selected third combobox should be filled as per the selected item. in same way fourth combobox.

Problem: when the item in the first combobox is selected all the remaining comboboxes controls are created duplicate and shown at the top of the page. the data is filling in those comoboboxes. what could be the problem? why is it so happening

I am using the master pages so that I have placed the script manager in master page.

Related code sample.

<tr>
                                    <th width="145" height="21" align="left" valign="top" scope="col">
                                    <asp:DropDownList ID="ProjectsCmb" runat="server" Width="140px"
                                        CssClass="formlines" Height="28px"
                                        onselectedindexchanged="ProjectsCmb_SelectedIndexChanged"
                                        AutoPostBack="True"  >
                                    </asp:DropDownList>&nbsp;&nbsp;
                                    </th>
                               <asp:UpdatePanel ID="UpdateFilterPanel" runat="server"  UpdateMode="Conditional" >
                                <ContentTemplate>
                                    <th width="145" height="21" align="left" valign="top" scope="col">
                                    <asp:DropDownList ID="SoftwareReleaseCmb" runat="server" Width="140px"
                                        CssClass="formlines"
                                        onselectedindexchanged="SoftwareReleaseCmb_SelectedIndexChanged"
                                        AutoPostBack="True" >
                                     </asp:DropDownList>&nbsp;&nbsp;</th>
                                </ContentTemplate>
                                <Triggers>
                                    <asp:AsyncPostBackTrigger ControlID="ProjectsCmb" />
                                </Triggers>
                             </asp:UpdatePanel>
                              <asp:UpdatePanel ID="UpdatePanel1" runat="server"  UpdateMode="Conditional" >
                                <ContentTemplate>
                                    <th width="145" height="21" align="left" valign="top" scope="col">
                                    <asp:DropDownList ID="PhasesCmb" runat="server" Width="140px" CssClass="formlines"
                                        onselectedindexchanged="PhasesCmb_SelectedIndexChanged" AutoPostBack="True">
                                    </asp:DropDownList>&nbsp;&nbsp; </th>
                              </ContentTemplate>
                                <Triggers>
                                    <asp:AsyncPostBackTrigger ControlID="SoftwareReleaseCmb" EventName="SelectedIndexChanged" />
                                </Triggers>
                             </asp:UpdatePanel>
                              <asp:UpdatePanel ID="UpdatePanel2" runat="server"  UpdateMode="Conditional" >
                                <ContentTemplate>
                                    <th width="145" height="21" align="left" valign="top" scope="col">
                                    <asp:DropDownList ID="RolesCmb" runat="server" Width="140px" CssClass="formlines"
                                       onselectedindexchanged="RolesCmb_SelectedIndexChanged"  AutoPostBack="True">
                                    </asp:DropDownList>&nbsp;&nbsp;</th>
                                </ContentTemplate>
                                <Triggers>
                                    <asp:AsyncPostBackTrigger ControlID="PhasesCmb" EventName="SelectedIndexChanged" />
                                </Triggers>
                             </asp:UpdatePanel>
                                    <th width="140" height="21" align="left" valign="top" scope="col">
                                    <asp:DropDownList ID="LanguagesCmb" runat="server" Width="130px"
                                        CssClass="formlines" >
                                    </asp:DropDownList></th>
                          </tr>
                          <tr>
                            <th valign="middle" align="center" colspan="5">&nbsp;
                            <asp:UpdateProgress ID="udProgress" runat="server"
                                DisplayAfter="100" Visible="true" DynamicLayout="true">
                                <ProgressTemplate>
                                    <asp:Image border="0" ImageUrl="~/Images/loading.gif" runat="server" />
                                </ProgressTemplate>
                            </asp:UpdateProgress>
                            </th>
                          </tr>