on main.rhtml, I have: <%= link_to_remote('add', :url=>{:action=>'openAdd'}, :update=>'addZone')-%> <div id="addZone"></div>
Don't use the :update option with rjs calls. That constructs an Ajax.Updater prototype object instead of the Ajax.Request object you need for rjs calls.
On the other hand, if you only need to update one html element, I'd leave the :update option and just return a regular partial template, pretty sure it's considerably faster.
Good Luck, Tim