Calendar won't display

[Typpex]

When i want to filter by datetime field, i can not display the calendar. It was working a few months back but it doesn't seem to be a regression because i tried to use other version of the gem but the problem remmain the same

ActionController::RoutingError - No route matches {:controller=>"will_filter/calendar"}:
(gem) actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:533:in raise_routing_error' (gem) actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:529:inrescue in generate'
(gem) actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:521:in generate' (gem) actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:562:ingenerate'
(gem) actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:587:in url_for' (gem) actionpack-3.2.11/lib/action_dispatch/routing/url_for.rb:148:inurl_for'
(gem) actionpack-3.2.11/lib/action_view/helpers/url_helper.rb:107:in url_for' (gem) actionpack-3.2.11/lib/action_view/helpers/form_tag_helper.rb:619:inblock in html_options_for_form'
(gem) actionpack-3.2.11/lib/action_view/helpers/form_tag_helper.rb:615:in tap' (gem) actionpack-3.2.11/lib/action_view/helpers/form_tag_helper.rb:615:inhtml_options_for_form'
(gem) actionpack-3.2.11/lib/action_view/helpers/form_tag_helper.rb:68:in form_tag' (gem) haml-4.0.3/lib/haml/helpers/action_view_mods.rb:132:inform_tag_with_haml'
(gem) haml-4.0.3/lib/haml/helpers/action_view_xss_mods.rb:18:in form_tag_with_haml_xss' (gem) will_filter-3.1.10/app/views/will_filter/calendar/index.html.erb:15:in__home_ubuntu__rvm_gems_ruby_______p____gems_will_filter________app_views_will_filter_calendar_index_html_erb___699857499__657661438'

The problem seem to be in will_filter/calendar/index.html.erb in form_tag({:controller => "/will_filter/calendar"}.

If i replace {:controller => "/will_filter/calendar"} by "will_filter/calendar" the calendar is displayed.