Help with form_for

Hello, I had an app running on RoR 1.1, now I'm migrating it to 2.1.

In a view I have:

<div id="user_management">
    <fieldset>
        <legend>Please log in</legend>
        <% form_for(:user, :url => sessions_path) do |f| %>
            <p>Username: <span class="notice"><%= flash[:notice]%></

</p>

            <%= f.text_field :username %>
            <p>Password:</p>
            <%= f.password_field :password %>
            <%= submit_tag 'Go!'%>
            <p>
                <label for='without_account_yet'>Register</label>
                <%= link_to 'New user?', new_user_path %>
            </p>
        <% end %>
    </fieldset>
</div>

Rendering it, the server gives this error, but I don't know what it
means. Any idea?

wrong argument type FalseClass (expected Proc)

Extracted source (around line #4):

1: <div id="user_management">
2: <fieldset>
3: <legend>Please log in</legend>
4: <% form_for(:user, :url => {:action => :create}) do |f| %>
5: <p>Username: <span class="notice"><%= flash[:notice]%></

</p>

6: <%= f.text_field :username %>
7: <p>Password:</p>

RAILS_ROOT: /home/eyp/workspace/lists
Application Trace | Framework Trace | Full Trace

(eval):2:in `protect_against_forgery?'
app/views/sessions/new.rhtml:4:in
`_run_erb_47app47views47sessions47new46rhtml'

/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_tag_helper.rb:431:in `extra_tags_for_form'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_tag_helper.rb:439:in `form_tag_html'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_tag_helper.rb:41:in `form_tag'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_helper.rb:252:in `form_for'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/base.rb:
338:in `send'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/base.rb:
338:in `execute'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template_handlers/compilable.rb:29:in `send'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template_handlers/compilable.rb:29:in `render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template.rb:35:in `render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template.rb:22:in `render_template'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/base.rb:
245:in `render_file'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:1108:in `render_for_file'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:841:in `render_with_no_layout'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
layout.rb:251:in `render_without_benchmark'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:51:in `render'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
core_ext/benchmark.rb:8:in `realtime'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:51:in `render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:1157:in `default_render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:1163:in `perform_action_without_filters'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
filters.rb:580:in `call_filters'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
filters.rb:573:in `perform_action_without_benchmark'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:68:in `perform_action_without_rescue'
/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:68:in `perform_action_without_rescue'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
rescue.rb:201:in `perform_action_without_caching'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
caching/sql_cache.rb:13:in `perform_action'
/usr/lib64/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
connection_adapters/abstract/query_cache.rb:33:in `cache'
/usr/lib64/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
query_cache.rb:8:in `cache'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
caching/sql_cache.rb:12:in `perform_action'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:529:in `send'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:529:in `process_without_filters'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
filters.rb:569:in `process_without_session_management_support'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
session_management.rb:130:in `process'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:389:in `process'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:149:in `handle_request'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:107:in `dispatch'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:104:in `synchronize'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:104:in `dispatch'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:120:in `dispatch_cgi'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:35:in `dispatch'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:76:in
`process'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:74:in
`synchronize'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:74:in
`process'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:159:in
`process_client'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in
`each'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in
`process_client'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`initialize'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`new'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in
`initialize'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in
`new'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/
configurator.rb:282:in `run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/
configurator.rb:281:in `each'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/
configurator.rb:281:in `run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:128:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/command.rb:
212:in `run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:281
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:502:in `load'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:502:in `load'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:354:in `new_constants_in'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:502:in `load'
/usr/lib64/ruby/gems/1.8/gems/rails-2.1.0/lib/commands/servers/
mongrel.rb:64
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:509:in `require'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:354:in `new_constants_in'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:509:in `require'
/usr/lib64/ruby/gems/1.8/gems/rails-2.1.0/lib/commands/server.rb:39
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
script/server:3

(eval):2:in `protect_against_forgery?'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_tag_helper.rb:431:in `extra_tags_for_form'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_tag_helper.rb:439:in `form_tag_html'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_tag_helper.rb:41:in `form_tag'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/helpers/
form_helper.rb:252:in `form_for'
app/views/sessions/new.rhtml:4:in
`_run_erb_47app47views47sessions47new46rhtml'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/base.rb:
338:in `send'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/base.rb:
338:in `execute'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template_handlers/compilable.rb:29:in `send'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template_handlers/compilable.rb:29:in `render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template.rb:35:in `render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
template.rb:22:in `render_template'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/base.rb:
245:in `render_file'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:1108:in `render_for_file'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:841:in `render_with_no_layout'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
layout.rb:251:in `render_without_benchmark'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:51:in `render'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
core_ext/benchmark.rb:8:in `realtime'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:51:in `render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:1157:in `default_render'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:1163:in `perform_action_without_filters'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
filters.rb:580:in `call_filters'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
filters.rb:573:in `perform_action_without_benchmark'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:68:in `perform_action_without_rescue'
/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
benchmarking.rb:68:in `perform_action_without_rescue'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
rescue.rb:201:in `perform_action_without_caching'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
caching/sql_cache.rb:13:in `perform_action'
/usr/lib64/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
connection_adapters/abstract/query_cache.rb:33:in `cache'
/usr/lib64/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/
query_cache.rb:8:in `cache'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
caching/sql_cache.rb:12:in `perform_action'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:529:in `send'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:529:in `process_without_filters'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
filters.rb:569:in `process_without_session_management_support'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
session_management.rb:130:in `process'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
base.rb:389:in `process'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:149:in `handle_request'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:107:in `dispatch'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:104:in `synchronize'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:104:in `dispatch'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:120:in `dispatch_cgi'
/usr/lib64/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatcher.rb:35:in `dispatch'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:76:in
`process'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:74:in
`synchronize'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:74:in
`process'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:159:in
`process_client'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in
`each'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in
`process_client'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`initialize'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`new'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in
`initialize'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in
`new'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/
configurator.rb:282:in `run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/
configurator.rb:281:in `each'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/
configurator.rb:281:in `run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:128:in
`run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/command.rb:
212:in `run'
/usr/lib64/ruby/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:281
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:502:in `load'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:502:in `load'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:354:in `new_constants_in'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:502:in `load'
/usr/lib64/ruby/gems/1.8/gems/rails-2.1.0/lib/commands/servers/
mongrel.rb:64
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:509:in `require'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:354:in `new_constants_in'
/usr/lib64/ruby/gems/1.8/gems/activesupport-2.1.0/lib/active_support/
dependencies.rb:509:in `require'
/usr/lib64/ruby/gems/1.8/gems/rails-2.1.0/lib/commands/server.rb:39
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
script/server:3

It seems that was nothing, today a new update for ruby 1.8.6 on Fedora
8 has resolved the issue! :). After updating, all wroked fine, again.