Solution : You have only one ruby version of ruby 1.9.2p180 (2011-02-18) [i386-mingw32] Problem Cause: Registry is still showing older version of RubyGems Solution Path: Remove all old version of ruby & dependencies (Note ensure to have all the back ups as your old apps on earlier ruby version which may not run after this solution)
Step 1: Go to command prompt & position at latest ruby 192 path Step 2: gem cleanup (Select Y for all prompts) Step 3: gem uninstall json Step 4: gem install json Step 5: Open user/app/GemFile and enter the line below under the line gem 'rails', '3.0.5' gem 'mongrel', '1.2.0.pre2' step 6: rails server Will boot from Mongrel & Rails 3.0.5