named route error: "failed to generate"

I don't know much about named routes so I'm looking for a clue here. If this isn't enough info to properly diagnose this, please tell me! The error is:

wap_event_disc_url failed to generate from {:invitation_id=>nil, :controller=>"wap", :all_comments=>true, :action=>"event_details", :token=>"wb", :id=>"603"}, expected: {:controller=>"wap", :action=>"event_details"}, diff: {:invitation_id=>nil, :all_comments=>true, :token=>"wb", :id=>"603"}

Extracted source (around line #9):

6: <% end %> 7: <%= render :partial => "comment", :collection => @comments %> 8: <% if @comments.size == 1 && subject.discussion_posts.count > 1 %> 9: <%= link_to "Show all #{subject.discussion_posts.count} comments", all_comments_url(subject) %> 10: <% end %> 11: <% if subject.is_a?(Place) || (subject.is_a?(Event) && (subject.owned_by_user || @invitation)) %> 12: <% if @comments.empty? %>

Here's the named route:

wap.wap_event_disc 'ev/:id/:token/:invitation_id/ all_comments', :action => 'event_details', :invitation_id => nil, :token => nil

One thing that does seem weird to me is that "all_comments_url" mentioned in the line as the error is NOT based on a named route. It's a method in the application_helper:

  def all_comments_url(subject)     if subject.is_a?(Place)       wap_listing_url(:id => subject, :all_comments => true, :anchor => 'message_board')     elsif subject.is_a?(Event)        wap_event_disc_url(:id => subject, :all_comments => true, :token => subject.wap_token, :invitation_id => params[:invitation_id], :anchor => 'message_board')     else       '' # 2 single quotes     end   end

(Does it clobber something in routes to name a method with _url at the end?)

Any ideas about how to handle this would be greatly appreciated. Thanks!

-Jason