Question: I have a textbox which when a users fills in the box and hits return does an auto postback and the update panel is there to just refresh that part of the page where the textbox is located.

I have attached to that textbox a requiredfieldvalidator which needs to fire if the user does not complete the box when they to move off to the next step in the wizard control.

The problem is that the validator is not firing, and I cannot see why? Is this a bug in ASP or do I need to do something else to validate inside an Update Panel?

Answer: 
I had the same problem with a modal and a UpdatePanel, **you have to add** in the requirefilevalidator property as a ValidationGroup="groupvalidationX", the same for the Button: 

```
<asp:UpdatePanel runat="server">
    <ContentTemplate>                                                       
        <asp:RequiredFieldValidator runat="server" ID="rfvtxtClave" ForeColor="Red" 
            ControlToValidate="txtClaveDependencia" Display="Dynamic" 
            ErrorMessage="Rellena este campo" SetFocusOnError="true" 
            ValidationGroup="validacionesDependencia">
        </asp:RequiredFieldValidator>

        <asp:TextBox runat="server" ID="txtClaveDependencia" MaxLength="10" 
            autocomplete="off" placeholder="Clave de la dependencia" 
            Style="display: inline" CssClass="form-control tb8">
        </asp:TextBox>
    </ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="btnGuardarDependencia" />
    </Triggers>
</asp:UpdatePanel>                                  
<asp:Button runat="server" ID="btnGuardarDependencia" 
    CssClass="btn btn-block botonAfirmacion" 
    ValidationGroup="validacionesDependencia" 
    Text="Guardar dependencia" CausesValidation="true" 
    OnClick="btnGuardarDependencia_Click" />

```
Because AutoPostBack is set to true, I believe the client-side validation process isn't able to fire when it needs to.

Try adding `CausesValidation="True"` to the TextBox.