Rails documentation generating error

Hi, I tried to generate Rails guides locally using following command

rake doc:guides

but rake aborats denoting following error message.

rake aborted!
Missing template credits.erb in view path /opt/local/lib/ruby/gems/1.8/

Also I tried to generate Rails doc using rake doc:rails it also fails.
rake aborted!
Don't know how to build task 'vendor/rails/railties/CHANGELOG'

My Rails version is 2.3.5.

Can anyone suggest how can I fix this problem?