sortable_element doesn't update div nor call onComplete function

I have a sortable UL with LIs in it

example:

<ul id="my_list">
<li id="my_list_1"></li>
<li id="my_list_2"></li>
<li id="my_list_3"></li>
</ul>
<%= sortable_element("my_list", { :complete => "alert ('hi')", :handle
=> "drag", :update => "menu", :url => { :action => "order_menu" } } )
%>

nothing happens, nothing at all, after I have changed the order and
dropped the item in its new position. Why?

thanks