RequiredFieldValidator with ValidationGroup doesn't validate

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VB

hi i am validation for gridview by using RequiredFieldValidator with ValidationGroup doesn't validate below is my code

<div id="sample_1_wrapper" class="dataTables_wrapper form-inline" role="grid">
                                    <asp:GridView ID="sample_2" runat="server" ShowFooter="true" AutoGenerateColumns="false"
                                        class="table table-striped table-bordered table-hover table-full-width">
                                        <Columns>
                                            <asp:BoundField DataField="RowNumber" HeaderText="Sr.No" />
                                            <asp:TemplateField HeaderText="IMEI Number">
                                                <ItemTemplate>
                                                    <asp:TextBox ID="IMEINumber" runat="server" /><br />
                                                    <asp:RequiredFieldValidator ID="RequiredFieldValidator1" ForeColor="red" runat="server"
                                                        ErrorMessage="This field is required" ControlToValidate="IMEINumber" ValidationGroup="GR" />
                                                </ItemTemplate>
                                            </asp:TemplateField>
                                            <asp:TemplateField HeaderText="Status">
                                                <ItemTemplate>
                                                    <asp:DropDownList ID="Status" runat="server">
                                                        <asp:ListItem Value="0">---Select---</asp:ListItem>
                                                        <asp:ListItem Value="1">Open</asp:ListItem>
                                                        <asp:ListItem Value="2">Closed</asp:ListItem>
                                                    </asp:DropDownList>
                                                    <br />
                                                    <asp:RequiredFieldValidator ID="rfvStatus" ForeColor="red" runat="server" ErrorMessage="This field is required"
                                                        ControlToValidate="Status" ValidationGroup="GR" />
                                                </ItemTemplate>
                                            </asp:TemplateField>
                                            <asp:TemplateField HeaderText="Valid Date">
                                                <ItemTemplate>
                                                    <div class="input-append" id="ui_date_picker_trigger">
                                                        <asp:TextBox ID="ValidDate" class="m-wrap medium" runat="server"></asp:TextBox>
                                                        <br />
                                                        <asp:RequiredFieldValidator ID="rfvui_date_picker_trigger" ForeColor="red" runat="server"
                                                            ErrorMessage="This field is required" ControlToValidate="ValidDate"
                                                            ValidationGroup="GR" />
                                                        <span class="add-on"><i class="icon-calendar"></i></span>
                                                    </div>
                                                </ItemTemplate>
                                                <FooterStyle HorizontalAlign="Right" />
                                                <FooterTemplate>
                                                    <asp:Button ID="AddRowButton" class="btn blue" runat="server" Text="Add New Row"
                                                        OnClick="ButtonAdd_Click" />
                                                </FooterTemplate>
                                            </asp:TemplateField>
                                        </Columns>
                                    </asp:GridView>
                                </div>
                            </div>
                            <div class="form-actions clearfix" style="padding-left: 400px;">
                                <asp:Button ID="btnSave" runat="server" Text="Save" class="btn blue button-next" OnClick="btnSave_Click"
                                    CausesValidation="true" ValidationGroup="GR" />
                            </div>