Undefined method `adapter_name' on GET request

I'm seeing the following in the development logs when I perform a GET request:

Processing "/posts" to */* (for 127.0.0.1 at 2010-01-17 18:12:05) [GET]

NoMethodError (undefined method `adapter_name' for {:engine=>#<Arel::Sql::Engine:0x1b33188 @ar=ActiveRecord::Base>}:Hash):
  app/controllers/posts_controller.rb:5:in `index'

In order to generate the my project, I performed the following steps:

$ rails blog-3.0.0
$ cd blog-3.0.0
$ script/generate scaffold post title:string blog:text
$ rake db:migrate
$ script/server

Now, navigate to the URL, http:://localhost:3000/posts, and one should be able to see the above message in the 'development.log' file.

I have the following configuration:

OS:  Mac OS 10.5.8 (PPC)
ruby 1.9.2dev (2010-01-18 trunk 26340) [powerpc-darwin9.8.0]

Lastly, my Gemfile contains the following:

gem "rails", "3.0.pre"

## Bundle edge rails:
# gem "rails", :git => "git://github.com/rails/rails.git"

## Bundle the gems you use:
gem "sqlite3-ruby", :require_as => "sqlite3"