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This post is about a Ruby on Rails problem that troubled me some time now. More specifically it's about Rails' gem dependencies which somehow do not work on Ubuntu 8.04. No matter which gem I added to the gem list in environment.rb, Rails raised a strange error as soon as the gem was installed:

/usr/lib/ruby/gems/1.8/gems/rails-2.1.0/lib/rails/plugin/locator.rb:91:in `add': wrong number of arguments (2 for 1) (ArgumentError)
  from /usr/lib/ruby/gems/1.8/gems/rails-2.1.0/lib/rails/plugin/locator.rb:91:in `plugins'
  from /usr/lib/ruby/gems/1.8/gems/rails-2.1.0/lib/rails/plugin/loader.rb:63:in `locate_plugins'
…

After searching around a bit I found the Rails ticket #293 at Lighthouse. The last post describes the error above and luckily explains the solution.

The Rubygem files are usually stored at /usr/local/lib/site_ruby/1.8. These are the up to date source files for Rubygems. I installed this Rubygems version from source but somehow an older version of Rubygems found it's way into the /usr/lib/ruby/1.8 directory. Now Rails used the obsolete Rubygems stuff from there which caused the error.

The solution

After deleting the /usr/lib/ruby/1.8/rubygems directory and the /usr/lib/ruby/1.8/rubygems.rb file everything went fine. Rails gem dependencies up and working. :)

If someone knows which deb packet contains these obsolete Rubygem files, please let me know or file a bug report at Luncepad.

Thanks to Dusty Doris for hunting down this bug and pointing out the solution. I hope this post will make the search a bit easier for people with the same problem.