当我运行rails -v时，我收到此错误。有人可以帮我理解发生了什么吗？
/Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/dependency.rb:298:in `to_specs': Could not find 'json' (~> 1.4) among 137 total gem(s) (Gem::LoadError)
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1265:in `block in activate_dependencies'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1254:in `each'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1254:in `activate_dependencies'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1236:in `activate'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1268:in `block in activate_dependencies'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1254:in `each'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1254:in `activate_dependencies'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1236:in `activate'
from /Users/buckleyjosh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_gem.rb:48:in `gem'
from /Users/buckleyjosh/.rvm/gems/ruby-1.9.3-p194/bin/rails:18:in `<main>'