I start with Mac OS X Leopard 10.5.2 with Rails 1.2.6 pre-installed:
cm-84:~ mikhailkovalev$ ruby -v
ruby 1.8.6 (2007-09-24 patchlevel 111) [universal-darwin9.0]
Works perfectly. I read a tip on Ruby on Rails — A web-app framework that includes everything needed to create database-backed web applications according to the Model-View-Controller (MVC) pattern. on
how to update Rails with gems:
cm-84:~ mikhailkovalev$ sudo gem update rails
Password:
Updating installed gems…
Attempting remote update of rails
Successfully installed rails-2.0.2
1 gem installed
Gems updated: rails
cm-84:~ mikhailkovalev$ rails -v
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/
1.8/rubygems.rb:379:in `report_activate_error’: RubyGem version error:
activesupport(1.4.2 not = 2.0.2) (Gem::LoadError)
…(further errors)
Very well, I search google and update gems, activesupport and
whatever:
cm-84:~ mikhailkovalev$ sudo gem update --system
cm-84:~ mikhailkovalev$ sudo gem update --source
http://gems.rubyonrails.org
The second line happens with some minor errors. Now:
cm-84:~ mikhailkovalev$ rails
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/
1.8/rubygems.rb:379:in `report_activate_error’: Could not find RubyGem
activeresource (= 2.0.2) (Gem::LoadError)
…
I want to
a) purge everything and do a clean re-install
b) is there a way out of this
c) back to php and see you in 2 years ? 
Mikhail Kovalev wrote:
The second line happens with some minor errors. Now:
cm-84:~ mikhailkovalev$ rails
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/
1.8/rubygems.rb:379:in `report_activate_error’: Could not find RubyGem
activeresource (= 2.0.2) (Gem::LoadError)
…
I want to
a) purge everything and do a clean re-install
b) is there a way out of this
c) back to php and see you in 2 years ? 
or…
d) read the error message more carefully…
it appears that your gem activeresource is the wrong version, you may
try
sudo gem update activeresource
although:
sudo gem update
should have picked up all dependencies by default…
I believe the --source and --system options are not needed for the
majority of cases…
If you keep plugging away at it, you will fix it… If you are ready to
go back to php after one slight hiccup then you should leave now as Ruby
is evolving very rapidly and tinkering at it is almost unavoidable…
hth
ilan
lets start with:
~$ gem list
you should have something like this:
actionmailer (2.0.2, 1.3.6, 1.3.3)
actionpack (2.0.2, 1.13.6, 1.13.3)
actionwebservice (1.2.6, 1.2.3)
activerecord (2.0.2, 1.15.6, 1.15.3)
activeresource (2.0.2)
activesupport (2.0.2, 1.4.4, 1.4.2)
rails (2.0.2, 1.2.6, 1.2.3)
+plus more…
Like mr Berci said if you look at the error you are missing
activesupport 2.0.2 try
~$ sudo gem install activesource -v=2.0.2
you could also just do:
~$ sudo remove all the active* and rails then
~$ sudo install rails
that should bring you back to square one…
FYI
~$ sudo gem update --system updates the gem system files
~$ sudo gem update updates the gems them self
to check for updates for the gems use
~$ sudo gem outdated
Hope this helps and welcome to the club…
I deleted everything with
sudo rm -r /System/Library/Frameworks/Ruby.framework/
sudo rm -r /Library/Ruby
sudo rm /usr/bin/ruby
sudo rm /usr/bin/gem
And installed gem from scratch with macports
sudo port install rb-rubygems
Took almost an hour. Now trying to update with:
sudo gem update --system
cm-84:~ mikhailkovalev$ sudo gem update --system
/opt/local/lib/ruby/vendor_ruby/1.8/rubygems/custom_require.rb:27:in
gem_original_require': no such file to load -- sources (LoadError) from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/custom_require.rb: 27:inrequire’
from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/
source_info_cache.rb:6
from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/custom_require.rb:
27:in gem_original_require' from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/custom_require.rb: 27:inrequire’
from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/remote_installer.rb:
12
from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/custom_require.rb:
27:in gem_original_require' from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/custom_require.rb: 27:inrequire’
from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems.rb:112:in
`manage_gems’
from /opt/local/bin/gem:10
False alarm, this fixed the problem
sudo port selfupdate
sudo port uninstall rb-rubygems
sudo port install rb-rubygems