Why my required field validator not validating in update pan

Delete Package

                                       class="control-group ">
 class="row-fluid">
 class="control-label col-sm-3">Package Period
 ID="UpdelPackPeriod" runat="server">

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

                                                     Value="Select">Select
 Value="Monthly">Monthly
 Value="Quarterly">Quarterly
 Value="HalfYearly">HalfYearly
 Value="Yearly">Yearly

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


 class="row-fluid">
 class="control-label col-sm-3">Select Package
 ID="UpdelPackName" runat="server">

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


 class="row-fluid">
 class="control-label col-sm-3">
 ID="upPackDelete" runat="server">
 ID="btnPackageDelete" runat="server"  class="btn btn-danger " Text="Dalete" ValidationGroup="PackageDeletion" onclick="btnPackageDelete_Click"/>


 ControlID="btnPackageDelete" EventName="Click" />