Unable to update from v.1.7.2 to v.1.8

    >sudo gem19 update --system          
Updating rubygems-update
ERROR:  Could not find gem rubygems-update (1.8.1)
ERROR:  While executing gem ... (Gem::GemNotFoundException)
    Could not find gem rubygems-update, (1.8.1)

I am able to checkout from SVN and compile a never version of ruby:

>ruby19 -v
ruby 1.9.3dev (2011-05-06 trunk 31449) [x86_64-darwin10.7.0]



>gem19 env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.7.2
  - RUBY VERSION: 1.9.3 (2011-05-06 patchlevel -1) [x86_64-darwin10.7.0]
  - INSTALLATION DIRECTORY: /usr/local/lib/ruby/gems/1.9.1
  - RUBY EXECUTABLE: /usr/local/bin/ruby19
  - EXECUTABLE DIRECTORY: /usr/local/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-10
  - GEM PATHS:
     - /usr/local/lib/ruby/gems/1.9.1
     - /Users/ericdp/.gem/ruby/1.9.1
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
     - "test_options" => {"auto_test_on_install"=>true, "install_development_dependencies"=>true, "upload_results"=>false, "force_install"=>true, "force_uninstall_on_failure"=>false}
  - REMOTE SOURCES:
     - http://rubygems.org/