You're using a custom install of ruby/rubygems : /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/source_index.rb
uninstall it, then reinstall redmine.
You're using a custom install of ruby/rubygems : lib/ruby/ site_ruby/ 1.9.1/rubygems/ source_ index.rb
/usr/local/
uninstall it, then reinstall redmine.