"uninitialized constant Authlogic"

Just followed the Authlogic tutorial. I am getting "uninitialized constant Authlogic" whe开发者_JAVA技巧n I try run the app. After searching, I can see that it has to do with gems/plugins but I can't find a solution.

Edit:

My UserSession model is:

class UserSession < Authlogic::Session::Base
end

Is it in your environment.rb file? If it is, did you restart your server?

If you're using Rails 3, is it in your Gemfile, and did you restart your server?

Most of all, did you install the gem?