date_select javascript_tag

Hi

this is ok

<label for="entry_nr_documento">Documento</label>
<%= text_field 'entry', 'nr_documento' %>
<!-- porta il focus sulla casella di testo -->
<%= javascript_tag render(:update) { |page|
page['entry_nr_documento'].focus } %>

this no

<label for="entry_data">Data</label>
<%= date_select 'entry', 'data', :order => [:day, :month, :year],
:start_year => 2006 %>
<%= javascript_tag render(:update) { |page| page['entry_data'].focus }
%>

err $("entry_data") has no properties

where is the mistake?.
thank