form_tag routing error in >= 1.2.2 ?

in resource routes, you normally have a pluralized model name:

map.resource :feedbacks

the you get:
1) feedbacks_path
# => GET/POST /feedbacks/
      (for getting a list of items or creating a new one.)
2) feedback_path(@feedback)
#=> GET/PUT/DELETE /feedbacks/ID_OF_GIVEN_FEEDBACK
      (for getting/updateing/deleting a specific record with a given
ID)
see the difference?
feedback_path <-> feedbackS_path

try this
<%= form_tag(feedbacks_path) %>

But also i think as your resource name is not pluralized something
gets mixed up somewhere along the way of these routing helpers, and
the error could still be there.
That it worked in 1.2.1 and not in 1.2.3 may be due to some code
changes in this area ....
try pluralizing your resource name in routes.rb too.