Gem::RemoteFetcher::FetchError error when do gem install rails

I am trying to install rails on Ubuntu 8.10, and met following errors. Please help me get through. The same error happens when do gem install heroku. Thanks for your help.

root@pierr-desktop:~# gem install rails ERROR: While executing gem ... (Gem::RemoteFetcher::FetchError) bad response 500 (http://gems.rubyforge.vm.bytemark.co.uk/gems/ actionpack-2.3.4.gem)

#other information root@pierr-desktop:~# ruby -v ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux] root@pierr-desktop:~# gem -v 1.2.0 root@pierr-desktop:~# gem list

*** LOCAL GEMS ***

activerecord (2.3.4) activesupport (2.3.4, 1.4.4) daemons (1.0.10) gem_plugin (0.2.3) rack (1.0.1) rake (0.8.7, 0.8.3) wirble (0.1.3)