thin 無法啟動？Missing the Rails 2.3.5 gem？

Thin 是比 Mongrel 更快的Web服务器

安裝 thin 非常簡單

sudo gem install thin

啟動方式

到rails的應用目錄下，打入
thin start

但啟動後卻會出現錯誤訊息

Missing the Rails 2.3.5 gem. Please `gem install -v=2.3.5 rails`, update your RAILS_GEM_VERSION setting in config/environment.rb for the Rails version you do have installed, or comment out RAILS_GEM_VERSION to use the latest version installed.

解決方式：移除rack 1.1.0，保留rack 1.0.1

sudo gem uninstall rack

若沒有 rack 1.0.1，可自行安裝

sudo gem install rack -v 1.0.1