Question

Why my buttons won’t work in update panel, but if I press “enter” key it’s working?

        <asp:ScriptManager ID="Sqrpt1" runat="server"></asp:ScriptManager>
        <asp:UpdatePanel UpdateMode="Always" ChildrenAsTriggers="true"  ID="updpan" runat="server"><ContentTemplate>
        <fieldset>
        <asp:Panel runat="server" ID="ClientSearchPa" DefaultButton="SearchClientPopup">
        <asp:TextBox ID="SearchClientBox" runat="server"></asp:TextBox>
&nbsp;<asp:Button ID="SearchClientPopup" runat="server" Text="Search" 
                onclick="SearchClientPopup_Click" /></asp:Panel>
        <br />
        <asp:ListBox ID="Clients" runat="server" Height="341px" Width="682px"></asp:ListBox>   

        <br />
        <br />
            <asp:Label ID="Label3" runat="server" Text="Label"></asp:Label>
           <asp:Button ID="ClientSelect" runat="server" OnClick="ClientSelect_Click" Text="button" /> 
           </fieldset> 
        </ContentTemplate>
        </asp:UpdatePanel> 

Answer 1

Your code is perfectly alright and button are firing event on server side change your some control values in server events. Your might not be noticing very fast response of ajax call

  protected void SearchClientPopup_Click(object sender, EventArgs e)
    {
        SearchClientBox.Text = "Hello ajax SearchClient clicked";
    }
    protected void ClientSelect_Click(object sender, EventArgs e)
    {
        SearchClientBox.Text = "Hello ajax ClientSelect cliecked ";
    }