Gem installation issues

I’m getting the following error when trying to install rspec:

scott-taylors-macbook-pro:dl_forms(specs) smt$ sudo gem install rspec
Password:
ERROR: Error installing rspec:
invalid gem format for
/usr/local/ruby_versions/1_8_6/lib/ruby/gems/1.8/cache/rspec-1.1.12.gem

Are the gems no longer hosted at rubyforge?

Scott