Use Validation Group
if want to display Error message on Button click. Like this.
<asp:RequiredFieldValidator ID="rqtxtQName" ValidationGroup="save" ControlToValidate="txtQueueName" runat="server" ErrorMessage="Some required field are missing." SetFocusOnError="True"Display="Dynamic"></asp:RequiredFieldValidator>
and use validation group on Button
also.
<asp:Button ID="btnSubmit" runat="server" Text="Submit" ValidationGroup="save" OnClick="btnSubmit_Click"/>
Hope it will helps.