cannot install ruby gems - zlib error

Question

I'm trying to install some Ruby Gems so I can use Ruby to notify me when I get twitter messages. However, after doing a gem update --system, I now get a zlib error every time I try and do a gem install of anything. below is the console output I get when trying to install ruby gems. (along with the output from gem environment).

C:\data\ruby>gem install twitter
ERROR:  While executing gem ... (Zlib::BufError)
    buffer error

C:\data\ruby>gem update --system
Updating RubyGems
ERROR:  While executing gem ... (Zlib::BufError)
    buffer error

C:\data\ruby>gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 1.2.0
  - RUBY VERSION: 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]
  - INSTALLATION DIRECTORY: c:/ruby/lib/ruby/gems/1.8
  - RUBY EXECUTABLE: c:/ruby/bin/ruby.exe
  - EXECUTABLE DIRECTORY: c:/ruby/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-mswin32-60
  - GEM PATHS:
     - c:/ruby/lib/ruby/gems/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://gems.rubyforge.org/