Updating gridview with validation

I have a gridview. when i click edit button it ll turn into a editable mode. i kept validation but not able to update.

Below is my code..

  <asp:GridView ID="GridView1" runat="server"
            ShowFooter="True" AutoGenerateColumns="false"
            OnRowCommand="GridView1_RowCommand" OnRowDeleting="GridView1_RowDeleting"
            OnRowEditing="GridView1_RowEditing" OnRowUpdating="GridView1_RowUpdating" DataKeyNames="Id"
           >

 <Columns>
                <asp:TemplateField HeaderText="EDIT">
                    <EditItemTemplate>
                        <asp:ImageButton ID="imgbtnUpdate" runat="server" CommandName="Update" ToolTip="Update" ImageUrl="~/IMAGES/tick_green_big.gif " />
                        <asp:ImageButton ID="imgbtnCancel" runat="server" CommandName="Cancel" ToolTip="Cancel" ImageUrl="~/IMAGES/cancel.gif" />
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:ImageButton ID="imgbtnEdit" runat="server" CommandName="Edit" ToolTip="Edit" ImageUrl="~/IMAGES/edit.jpeg" />
                    </ItemTemplate>
                    <FooterTemplate>
                        <asp:ImageButton ID="imgbtnAdd" runat="server" CommandName="Add" ToolTip="Add" ImageUrl="~/IMAGES/ADD.jpeg" />
                    </FooterTemplate>
                </asp:TemplateField>
            </Columns>

<Columns>
                <asp:CommandField ShowSelectButton="True" />
                <asp:TemplateField HeaderText="Name">
                    <EditItemTemplate>
                        <asp:HiddenField ID="hdnId" runat="server" Value='<%# Bind("Id") %>' />
                        <asp:TextBox ID="txtname" runat="server" Text='<%#Eval("Name") %>' />
                          <asp:RegularExpressionValidator ID="regname" runat="server"
                ErrorMessage="Enter characters" Display="Dynamic"
                ControlToValidate="txtname" ValidationExpression="[a-zA-Z]" ForeColor="#993333"></asp:RegularExpressionValidator>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:HiddenField ID="hdnId" runat="server" Value='<%# Bind("Id") %>' />
                        <asp:Label ID="lblname" runat="server" Text='<%#Eval("Name") %>' />
                    </ItemTemplate>
                    <FooterTemplate>
                        <asp:TextBox ID="txtftrname" runat="server" />
                    </FooterTemplate>
                </asp:TemplateField>
            </Columns>

Text in Bold ---> regular expression i kept. update not working if i use validation. without validation code works fine.

Help me please...