Ruby Gems System Update Error

I've got an old version of rubygems on my server and so I went to update
it but I get a very unhelpful error message ('Killed') - any clues?

~ :
  ... gem -v
0.9.0
~ :
  ... gem update --system
Updating RubyGems...
Bulk updating Gem source index for: http://gems.rubyforge.org
Killed

···

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Posted via http://www.ruby-forum.com/.

Two shots in the blue:

1. Maybe a permissions problem. Did you run it as root?

2. I think gem update --system doesn't work between all rubygems versions.
Try to download and install from the tarball.