could not run generate statements after installing rails plugin - ruby-on-rails-3

Question

I tried installing the paperclip plugin from my rails project root directory, by
rails plugin install http://github.com/thoughtbot/paperclip.git
vendor/plugins/paperclip was created successfully. But after that i could not run any generate (rails generate scaffold ) commands . I'm getting error as
D:\rr\pr2>rails g scaffold car name:string
D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/active_support/d
ependencies.rb:240:in `require': no such file to load -- cocaine (LoadError)
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:240:in `block in require'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:223:in `block in load_dependency'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:640:in `new_constants_in'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:223:in `load_dependency'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:240:in `require'
from D:/rr/pr2/vendor/plugins/paperclip/lib/paperclip.rb:45:in `<top (re
quired)>'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:240:in `require'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:240:in `block in require'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:223:in `block in load_dependency'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:640:in `new_constants_in'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:223:in `load_dependency'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/activesupport-3.1.0/lib/act
ive_support/dependencies.rb:240:in `require'
from D:/rr/pr2/vendor/plugins/paperclip/init.rb:1:in `block in <class:Pl
ugin>'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/pl
ugin.rb:80:in `eval'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/pl
ugin.rb:80:in `block in <class:Plugin>'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/in
itializable.rb:25:in `instance_exec'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/in
itializable.rb:25:in `run'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/in
itializable.rb:50:in `block in run_initializers'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/in
itializable.rb:49:in `each'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/in
itializable.rb:49:in `run_initializers'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/ap
plication.rb:92:in `initialize!'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/ra
iltie/configurable.rb:30:in `method_missing'
from D:/rr/pr2/config/environment.rb:5:in `<top (required)>'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/ap
plication.rb:78:in `require'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/ap
plication.rb:78:in `require_environment!'
from D:/sprtcr/ruby/lib/ruby/gems/1.9.1/gems/railties-3.1.0/lib/rails/co
mmands.rb:22:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'

Answer 1

By installing this gem as a plugin, you're not going to get the dependencies that the gem requires. The paperclip gem depends on another gem called cocaine.
I would really recommend installing the paperclip gem by putting it into your Gemfile and running bundle install.
This is why you should use gems rather than plugins.