TypeError: Effect[effect_class] when using block form of link_to helper

Anyone have any idea why I'm getting this error when using the block
form of the link_to helper in Rails 2.0.1? I'm essentially using the
exact same code as in the Rails doc example, but no luck. Any help
would be appreciated.

Sorry, meant link_to_function, not link_to.

Ryan,

I'm using the following code in my .rhtml file:

<%=
    link_to_function("show", nil, :id => "more_link", :class =>
"expand_collapse") do |page|
      page[:user_listings].visual_effect :toggle_appear
      page[:more_link].replace_html "hide"
    end
%>

I should have mentioned that 'user_listings' is the id of a div
defined on my page.

It's in the Rails docs here: http://api.rubyonrails.org/classes/ActionView/Helpers/JavaScriptHelper.html#M001048.
Specifically, this part:

"The function argument can be omitted in favor of an update_page
block, which evaluates to a string when the template is rendered
(instead of making an Ajax request first)."

Followed by an example similar to the one I posted.