Radiant Install on Dreamhost

I have been following this guide:

And I get the error:

/home/my_id/.gems/gems/radiant-0.9.1/vendor/rails/activesupport/libive_support/dependencies.rb:55:
uninitialized constant ActiveSupport::Dependes::Mutex (NameError)

when I try to run:

radiant mysite.com

Right now I am at Rails 3.0.3 which may be causing the problem (it won’t
let me uninstall it). If that is, how can I run an older version? If
not, what else can I do? I am stumped - thank you.