OnClick of a Button does not enter the ASP.NET C # event

I have a problem with a button, it has an OnClick event but it does not enter the function that is programmed in C #.

 protected void Page_Load(object sender, EventArgs e)
    {
        btn_agregarCentro.Click += new EventHandler(this.btn_agregarCentro_Click);
    }
protected void btn_agregarCentro_Click(object sender, EventArgs e)
    {
        //no entra al evento
        Button cliqueado = (Button)sender;
        cliqueado.Text = "clickeado";
        cliqueado.Enabled = false;
    }

Above the code that is in c #, in the asp I have the following button:

    <%@ Page Title="" Language="C#" MasterPageFile="~/Program.Master" AutoEventWireup="true" CodeBehind="Compras.aspx.cs" Inherits="Program.Compras.ComprasIn" EnableEventValidation="false" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <asp:ScriptManager ID ="ScriptManager1" runat="server" EnablePageMethods="true"></asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <section class="content">
                <div class="row">
                    <div class="col-md-4">
                        <div class="box box-danger">
                            <div class="box-body">
                                <div class="row">
                                    <div class="col-md-12">
                                        <h4>Procentajes</h4>
                                        <form class="form-horizontal">
                                            <div class="form-group">
                                                <div class="col-sm-8">
                                                    <asp:Button ID="btn_agregarCentro" CssClass="btn btn-default" Text="Agregar" OnClick="btn_agregarCentro_Click" runat="server"/>
                                                </div>
                                            </div>
                                        </form>
                                    </div>
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </section>
        </ContentTemplate>
    </asp:UpdatePanel>
</asp:Content>

The button never enters the function

  

btn_aggregateClick_Center

What could be the problem?