Problem with loading acts_as_authenticated plugin

I currently develop a little app, and i installed the
acts_as_authenticated plugin
Everything worked fine til yesterday evening. While working on CSS
sheet, then testing iteratively : nothing worked.
Checking the development.log file in my Rails app , it shows:

NameError (uninitialized constant
dependencies.rb:477:in `const_missing’

It comes from the :
include AuthenticatedSystem
declared in my application.rb file (inside the class)

When commenting it, no more problems.

It seems the plugin’s libraries are not loaded.
Wht i do not understand, is i have another plugin installed :
acts_as_taggable, which works perfectly.

After searching with Google, i had some configurations tricks in
environment.rb >
Dependencies.log_activity = true

But nothing changes

Any help is needed

PS : my environment is :
Mac OS X 10.4.9
Ruby 1.8.2
Rails 1.2.3


I resolved the problem with the help of some folks on irc.
In fact, after several reinstallation of the plugin, i should run the
script :
./script/generate authenticated user account

It should create a folder /lib into : /vendor/plugins/
acts_as_authenticated, including the authenticated_system.rb file

But, this folder has been created in the /log folder.
Moving the lib folder to the plugin root folder did the trick.