Cannot find gem for Rails

I've been working with Ruby on Rails through Locomotive for the past year or so, but for this particular task, I need to run a Rails application outside the Locomotive environment. I can create a Rails application just fine, using "rails my_app", and it boots up properly in Mongrel, but whenever I run rake to migrate my database, I get the following error:

Cannot find gem for Rails ~>1.2.2.0:     Install the missing gem with 'gem install -v=1.2.2 rails', or     change environment.rb to define RAILS_GEM_VERSION with your desired version.

I have tried everything I can think of: re-installing Rails with gems by copying-and-pasting the line above into the terminal (as superuser of course), pasting the rails_gem = Gem.cache.search('rails'... line can't get rake to run. Does anyone have any tips?

Thank you very much, -Ryan

System configuration:

G4 PowerBook, with OS X 10.4.8. I've installed Ruby, Gems, and Rails:   rschenk$ ruby -v   ruby 1.8.5 (2006-12-25 patchlevel 12) [powerpc-darwin8.8.0]   rschenk$ gem -v   0.9.2   rschenk$ rails -v   Rails 1.2.2

When I type ./script/about:   About your application's environment   Ruby version 1.8.5 (powerpc-darwin8.8.0)   RubyGems version 0.9.2   Rails version 1.2.2   Active Record version 1.15.2   Action Pack version 1.13.2   Action Web Service version 1.2.2   Action Mailer version 1.3.2   Active Support version 1.4.1   Application root /Users/rschenk/Desktop/ simple_rails_test   Environment development   Database adapter mysql