form urls and activeresource object

I have an update form that looks like this:

<% form_for @article do |f| %>   <p>     <b>Title</b><br />     <%= f.text_field :title %>   </p>    <p>     <%= f.submit "Update" %>   </p>

and when I try to update it doesn't work because it prints this in the html form:

<form action="/articles/%23%3CArticle:0xb6951170%3E" class="edit_article" id="edit_article_1" method="post"><div style="margin:0;padding:0"><input name="_method" type="hidden" value="put" />

so rails thinks that my article id is "%23%3CArticle:0xb6951170%3E", any idea how to make it work?

thanx in advance