Error message: ActionView::TemplateError (No :secret given t

Hi all

I am getting this error message on the log, and I do not unserstand it.

I am using rails 2.0. Please advice

ActionView::TemplateError (No :secret given to the #protect_from_forgery
call. Set that or use a session store capable of generating its own
keys (Cookie Session Store).) on line #8 of store/index.html.erb:
5: <h3><%= h(product.title) %></h3>
6: <%= product.description %>
7: <span class="price" ><%= number_to_currency(product.price) %></span>
8: <%= button_to "Add to cart", :action => :add_to_cart, :id=> product
9: </div>
10: <% end %>