Ever get this gem when running a Rails 2.3.5 application with Thin?
/Users//config/../vendor/rails/railties/lib/initializer.rb:271:in `require_frameworks': can't activate rack (~> 1.0.1, runtime) for [], already activated rack-1.1.0 for ["thin-1.0.0"] (RuntimeError)
from /Users//config/../vendor/rails/railties/lib/initializer.rb:134:in `process'
from /Users//config/../vendor/rails/railties/lib/initializer.rb:113:in `send'
from /Users//config/../vendor/rails/railties/lib/initializer.rb:113:in `run'
from /Users//config/environment.rb:13
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `require'
from /Library/Ruby/Gems/1.8/gems/thin-1.0.0/lib/rack/adapter/rails.rb:31:in `load_application'
from /Library/Ruby/Gems/1.8/gems/thin-1.0.0/lib/rack/adapter/rails.rb:23:in `initialize'
... 6 levels...
from /Library/Ruby/Gems/1.8/gems/thin-1.0.0/lib/thin/runner.rb:139:in `run!'
from /Library/Ruby/Gems/1.8/gems/thin-1.0.0/bin/thin:6
from /usr/bin/thin:19:in `load'
from /usr/bin/thin:19
Disappointing to be sure, but there’s a simple fix I found here. Thin will try to load the latest version of Rack that you have installed, but Rails specifically asks for 1.0.1. You can’t have 2 versions of it running at the same time, so RubyGems pukes.
The simple solution is to uninstall Rack 1.1.0. If that isn’t an option for you, dang. There’s always this rails ticket you could go fix and make a big name for yourself in the community. 
