rails 3 undefined method `_index_path' when using form_for

I have recently created a new rails 3 application, using the code that I wrote for Rails 2, upgrading it at the same time to match the new API.

I have the following code:

#routes.rb:
FtpMgmt::Application.routes.draw do
    resources :accounts
    root :to => "accounts#index"
    match ':controller(/:action(/:id(.:format)))'
end

#new.html.erb
<% form_for(@account) do |f| %>
...
<% end %>

#accounts_controller.rb
class AccountsController < ApplicationController
    respond_to :html, :xml, :json
    def new
        @account = Accounts.new
        respond_with(@account)
    end
end

The error I get is:

Showing /opt/rails/ftp_mgmt/app/views/accounts/new.html.erb where line #3 raised: 
undefined method `accounts_index_path' for #<#<Class:0x0000000a28a758>:0x0000000a269b70>

Do you have any ideas how I can fix this?