【Ruby on Rails】以下のエラーが出る理由と対応策を教えてください。

$ ruby script/server
=> Booting WEBrick...
/usr/lib/ruby/gems/1.8/gems/rails-1.2.3/lib/commands/servers/webrick.rb:11: warning: already initialized constant OPTIONS
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require': no such file to load -- gettext/rails (MissingSourceFile)
from /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
from ./script/../config/../vendor/rails/activesupport/lib/active_support/dependencies.rb:495:in `require'
from ./script/../config/../vendor/rails/activesupport/lib/active_support/dependencies.rb:342:in `new_constants_in'
from ./script/../config/../vendor/rails/activesupport/lib/active_support/dependencies.rb:495:in `require'
from ./script/../config/../config/environment.rb:63
from /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require'
from /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
from ./script/../config/../vendor/rails/activesupport/lib/active_support/dependencies.rb:495:in `require'
... 7 levels...
from ./script/../config/../vendor/rails/activesupport/lib/active_support/dependencies.rb:495:in `require'
from