Trying to install Ruby on Rails on OSX and I get a Gem::RemoteSourceException

What is going on when I get this "HTTP Response 403" error?

I am trying to setup Ruby on Rails on OS X 10.5.8 with XCode 3.1.4:

Boston:$ ruby --version
ruby 1.8.6 (2008-08-11 patch开发者_JAVA技巧level 287) [universal-darwin9.0]
Boston:$ gem --version
1.0.1

Boston:$ sudo gem update --system
Password:
Updating RubyGems...
ERROR:  While executing gem ... (Gem::RemoteSourceException)
    HTTP Response 403 fetching http://gems.rubyforge.org/yaml

Boston:$ sudo gem install rubygems-update
ERROR:  While executing gem ... (Gem::RemoteSourceException)
    HTTP Response 403 fetching http://gems.rubyforge.org/yaml

I can't find a single specific reference online to the 403 error on OS X. I have tried adding alternate source repositories and I get the same error.

Solution Based on @Phil's Answer

I downloaded rubygems-1.3.5.zip from http://rubyforge.org/frs/?group_id=126 and unzipped the file.

Then I cd'd into the rubygems-1.3.5 directory and ran

 Boston:rubygems-1.3.5$ sudo ruby setup.rb
 RubyGems 1.3.5 installed

Thanks @Phil!

I just ran into this. I assume the gemcutter switchover broke old versions of rubygems (i.e. the version that comes with Leopard).

I fixed the problem by manually upgrading rubygems via http://rubyforge.org/frs/?group_id=126.