Uninitialized constant ActiveSupport::Dependencies::Mutex (NameError)

This error may occur to run older Rails application for conflicting with rubygems version. After a long googling I’ve come out in to following three solutions:

Using Bundler.:
Click here if you are interested to see the solution.

Changing rubygems version:

  • Downgrade the rubygems to an earlier version using gem update --system {version}
  • Add “require ‘thread’” in to – Rakefile, script/server and config/environment.rb

Upgrade Rails:
Upgrade application in to Rails 3 though it’s very hard to do for existing/running rails application.

For me, I was trying to run Rails 2.3.5 application where my system had rubygems 1.8.2. I’ve changed the rubygems version in to 1.7.2 as mentioned above and everything works fine.

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