How to use label for in an ASP.Net webform?

You should use the <asp:Label...> as detailed in this blog post on Haacked

<asp:Label id="label" AssociatedControlId="txtPais" Text="Pais:" runat="server" />
<asp:TextBox id="txtPais" runat="server" CssClass="textInput" />

This should convert correctly with the ID being converted.