Last year I blogged about where to get up-to-date Ruby packages for Ubuntu.
The PPA I suggested hasn’t been updated in a while, and there are a few gems that require the latest version of RubyGems to work correctly (Rails, i’m looking at you).
I suggest you remove the PPA and add this to your
dapper depending on what release you need.
Then do an
apt-get update && apt-get remove rubygems && apt-get install rubygems, and you’ll be upgraded to the latest version of RubyGems.