Why my required field validator not validating in update pan

Question

Delete Package

                                      <div class="control-group ">
<div class="row-fluid">
<label class="control-label col-sm-3">Package Period</label>
<asp:UpdatePanel ID="UpdelPackPeriod" runat="server"><ContentTemplate>      

This is my first dropdown list which I have put in update panel with required field validator.

                                                    <asp:ListItem Value="Select">Select</asp:ListItem>
<asp:ListItem Value="Monthly">Monthly</asp:ListItem>
<asp:ListItem Value="Quarterly">Quarterly</asp:ListItem>
<asp:ListItem Value="HalfYearly">HalfYearly</asp:ListItem>
<asp:ListItem Value="Yearly">Yearly</asp:ListItem>
</asp:dropdownlist>

This is my first dropdown's required field validator which also have put in update panel. 

                                          </div>
<div class="row-fluid">
<label class="control-label col-sm-3">Select Package</label>
<asp:UpdatePanel ID="UpdelPackName" runat="server"><ContentTemplate>

This is my second dropdown list which I have put in another update panel with required field validator.
Select

                                          </div>
<div class="row-fluid">
<label class="control-label col-sm-3"></label>
<asp:UpdatePanel ID="upPackDelete" runat="server"><ContentTemplate>
<asp:Button ID="btnPackageDelete" runat="server"  class="btn btn-danger " Text="Dalete" ValidationGroup="PackageDeletion" onclick="btnPackageDelete_Click"/>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="btnPackageDelete" EventName="Click" />
</Triggers>
</asp:UpdatePanel>
</div>
</div>
</div>
</div>
</div>
</div>