Currently there is a hard coded dependency in rubygem-rubigen which tries to pull in activesupport 2.3.5.
See /usr/lib/ruby/gems/1.8/gems/rubigen-1.5.4/lib/rubigen.rb for more info
This needs to be removed/updated as activesupport in Fedora has since been updated to 3.0.x
This has been fixed in rubigen 1.5.6 which was just pushed / built. Closing