problem with confirm message when using commmand button

I have a gridview that I used command button for it ,I want to when i click on delete button see a confirm ,I see , but when i click in update button,it must be go to edit mode but I see this error :
here is my code:
gridview sourece:
<asp:Button ID="Button5" runat="server" CausesValidation="True" CommandName="Update"
                    Text="update" />&nbsp;<asp:Button ID="Button6" runat="server" CausesValidation="False"
                        CommandName="Cancel" Text="cancel" />
            </EditItemTemplate>
        &n ...