<atlas:ScriptManager ID="sm" runat="server" EnablePartialRendering="true" />
<atlas:UpdatePanel ID="up" runat="server">
<ContentTemplate>
<asp:Label ID="Label1" runat="server" Text="Hallo" Visible="false" />
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
</ContentTemplate>
</atlas:UpdatePanel>
protected void Button1_Click(object sender, EventArgs e)
{
Label1.Visible = true;
}
So mach ich das immer. Wofür brauchst du den HTML-Code?