Rails beginner guide http://guides.rubyonrails.org/getting_started.html

Thanks for a great tutorial. However, I ran into the following error
after I had finished building the comments. What could be wrong? I am
using Rails version 2.3.4.

post_comment_url failed to generate from
{:action=>"show", :post_id=>#<Post id: 1, title: "11", body: "body1",
created_at: "2009-11-13 16:42:33", updated_at: "2009-11-13
16:42:33">, :id=>#<Comment id: nil, commenter: "boo", body: "boo",
post_id: 1, created_at: nil, updated_at:

, :controller=>"comments"}, expected:

{:action=>"show", :controller=>"comments"}, diff: {:post_id=>#<Post
id: 1, title: "11", body: "body1", created_at: "2009-11-13 16:42:33",
updated_at: "2009-11-13 16:42:33">, :id=>#<Comment id: nil, commenter:
"boo", body: "boo", post_id: 1, created_at: nil, updated_at: nil>}