validation in edittemplate and footertemplate of gridview

I am using a Gridview to Edit, Delete, and Insert (thru the footer).   I am  tryng to usr required field validationg a column called qty .When I insert a record through footer validating is working fine.(Add button in footer template)

But when I edit a record and it is validating both footertemplate and edititemtemplate.

<asp:GridView ID="grdMatReq" runat="server" AutoGenerateColumns="False"

        ShowFooter="True" Font-Size="Small"

        AllowPaging ="True" onrowediting="EditMatReq"

        OnPageIndexChanging = "OnPaging" CssClass="width-1050 center-margin center-text"

        onrowupdating="UpdateMatReq"  onrowcancelingedit="CancelEdit"

        onrowdatabound="grdMatReq_RowDataBound" CellPadding="4" ForeColor="#333333"

        GridLines="None" >

          <AlternatingRowStyle BackColor="White" ForeColor="#284775" />

          <Columns>

        <asp:TemplateField  ItemStyle-Width = "0px" Visible="false" >

            <ItemTemplate>

              <asp:Label ID="lblsno" Visible="false" runat="server" Text='<%# Eval("sno")%>'></asp:Label>

            </ItemTemplate>

            <FooterTemplate>

            </FooterTemplate>

<ItemStyle Width="0px"></ItemStyle>

        </asp:TemplateField>

        <asp:TemplateField   HeaderText = "work order no">

        <headertemplate>

     work order no<br />رقمالأمر

    </headertemplate>

            <ItemTemplate>

                <asp:Label ID="lblwork_order_no" runat="server" Text='<%# Eval("work_order_no")%>'></asp:Label>

            </ItemTemplate>

            <EditItemTemplate>

                <asp:TextBox ID="txtEditwork_order_no"  runat="server" Text='<%# Eval("work_order_no")%>'></asp:TextBox>

            </EditItemTemplate> 

            <FooterTemplate>

            </FooterTemplate>

        </asp:TemplateField>

        <asp:TemplateField   HeaderText = "material_req">

         <headertemplate>

     material_req<br />الموادالمطلوبة

    </headertemplate>

            <ItemTemplate>

                <asp:Label ID="lblmaterial_req" runat="server" Visible="false" Text='<%# Eval("material_req")%>'></asp:Label>

                 <asp:DropDownList ID="dd_type" runat="server" ></asp:DropDownList>

            </ItemTemplate>

            <EditItemTemplate> 

               <asp:Label ID="lblmaterial_req" runat="server" Visible="false" Text='<%# Eval("material_req")%>'></asp:Label>

                <asp:DropDownList ID="dd_type" runat="server" ></asp:DropDownList>

            </EditItemTemplate> 

            <FooterTemplate>

                <asp:DropDownList ID="dd_type" runat="server" ></asp:DropDownList>

            </FooterTemplate>

        </asp:TemplateField>

         <asp:TemplateField   HeaderText = "Quantity">

         <headertemplate>

     Quantity<br /> الكمية

    </headertemplate>

            <ItemTemplate>

                <asp:Label ID="lblqty" runat="server" Text='<%# Eval("qty")%>'></asp:Label>

            </ItemTemplate>

            <EditItemTemplate>

               <asp:TextBox ID="txtEditqty"  runat="server" Text='<%# Eval("qty")%>'></asp:TextBox>

               <asp:RequiredFieldValidator ID="RFV_txtEditqty" runat="server"

                    ControlToValidate="txtEditqty" Display="Dynamic" ErrorMessage="Compulosry" SetFocusOnError="true"

                                             >*</asp:RequiredFieldValidator>

            </EditItemTemplate> 

            <FooterTemplate>

                <asp:TextBox ID="txtInsertqty"  runat="server"></asp:TextBox>

                <asp:RequiredFieldValidator ID="RFV_txtInsertqty" runat="server"

                    ControlToValidate="txtInsertqty" Display="Dynamic" ErrorMessage="Compulosry" 

                    SetFocusOnError="True" >*</asp:RequiredFieldValidator>

            </FooterTemplate>

        </asp:TemplateField>

        <asp:TemplateField   HeaderText = "unit_of_issue">

        <headertemplate>

     Unit Of Issue<br />وحدةالصرف

    </headertemplate>

            <ItemTemplate>

                <asp:Label ID="lblunit_of_issue" runat="server" Text='<%# Eval("unit_of_issue")%>'></asp:Label>

            </ItemTemplate>

            <EditItemTemplate>

                <asp:TextBox ID="txtEditunit_of_issue"  runat="server" Text='<%# Eval("unit_of_issue")%>'></asp:TextBox>

            </EditItemTemplate> 

            <FooterTemplate>

                <asp:TextBox ID="txtunit_of_issue"  runat="server"></asp:TextBox>

            </FooterTemplate>

        </asp:TemplateField>

        <asp:TemplateField   HeaderText = "variance_type">

        <headertemplate>

     Variance Type<br />الاختلافـــــــاتالنوع

    </headertemplate>

            <ItemTemplate>

                <asp:Label ID="lblvariance_type" runat="server" Text='<%# Eval("variance_type")%>'></asp:Label>

            </ItemTemplate>

            <EditItemTemplate>

                <asp:TextBox ID="txtEditvariance_type"  runat="server" Text='<%# Eval("variance_type")%>'></asp:TextBox>

            </EditItemTemplate> 

            <FooterTemplate>

                <asp:TextBox ID="txtvariance_type"  runat="server"></asp:TextBox>

            </FooterTemplate>

        </asp:TemplateField>

        <asp:TemplateField   HeaderText = "variance_quantity">

        <headertemplate>

     Variance Quantity<br />الاختلافـــــــاتالكمية

    </headertemplate>

            <ItemTemplate>

                <asp:Label ID="lblvariance_quantity" runat="server" Text='<%# Eval("variance_quantity")%>'></asp:Label>

            </ItemTemplate>

            <EditItemTemplate>

                <asp:TextBox ID="txtEditvariance_quantity"  runat="server" Text='<%# Eval("variance_quantity")%>'></asp:TextBox>

            </EditItemTemplate> 

            <FooterTemplate>

                <asp:TextBox ID="txtvariance_quantity"  runat="server"></asp:TextBox>

            </FooterTemplate>

        </asp:TemplateField>

        <asp:TemplateField ItemStyle-Width = "30px" >

            <ItemTemplate>

                <asp:LinkButton ID="lnkRemove" runat="server" CommandArgument = '<%# Eval("sno")%>'

                 OnClientClick = "return confirm('Do you want to delete?')"

                 OnClick = "DeleteProduct"><img alt="Delete" src="" /></asp:LinkButton>

            </ItemTemplate>

             <FooterTemplate>

             <asp:Button ID="btnAdd" runat="server" Text="Add"  CssClass="art-button" OnClick = "AddNewMaterial" />

            </FooterTemplate>

<ItemStyle Width="30px"></ItemStyle>

        </asp:TemplateField>

        <asp:CommandField ItemStyle-Width="30" ButtonType="Link"    ShowEditButton="True" >

<ItemStyle Width="30px"></ItemStyle>

              </asp:CommandField>

       </Columns>

                                          <EditRowStyle BackColor="#999999" />

          <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />

          <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />

          <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />

          <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />

          <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />

          <SortedAscendingCellStyle BackColor="#E9E7E2" />

          <SortedAscendingHeaderStyle BackColor="#506C8C" />

          <SortedDescendingCellStyle BackColor="#FFFDF8" />

          <SortedDescendingHeaderStyle BackColor="#6F8DAE" />

                                          </asp:GridView>