Ruby on Rails - rspec Error `to_specs': Could not find 'rspec-core'

$ rspec spec/requests/shipping_methods/table_rate_upload_spec22.rb

/usr/local/lib/site_ruby/2.1.0/rubygems/dependency.rb:315:in `to_specs': Could not find 'rspec-core' (>= 0) among 44 total gem(s) (Gem::LoadError)
Checked in 'GEM_PATH=/home/railseng/.rvm/gems/ruby-2.0.0-p643:/home/railseng/.rvm/gems/ruby-2.0.0-p643@global', execute `gem env` for more information
	from /usr/local/lib/site_ruby/2.1.0/rubygems/dependency.rb:324:in `to_spec'
	from /usr/local/lib/site_ruby/2.1.0/rubygems/core_ext/kernel_gem.rb:64:in `gem'
	from /usr/local/bin/rspec:22:in `<main>'

$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 2.4.8
  - RUBY VERSION: 2.0.0 (2015-02-25 patchlevel 643) [i686-linux]
  - INSTALLATION DIRECTORY: /home/railseng/.rvm/gems/ruby-2.0.0-p643
  - RUBY EXECUTABLE: /home/railseng/.rvm/rubies/ruby-2.0.0-p643/bin/ruby
  - EXECUTABLE DIRECTORY: /home/railseng/.rvm/gems/ruby-2.0.0-p643/bin
  - SPEC CACHE DIRECTORY: /home/railseng/.gem/specs
  - SYSTEM CONFIGURATION DIRECTORY: /home/railseng/.rvm/rubies/ruby-2.0.0-p643/etc
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-linux
  - GEM PATHS:
     - /home/railseng/.rvm/gems/ruby-2.0.0-p643
     - /home/railseng/.rvm/gems/ruby-2.0.0-p643@global
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     - /usr/local/heroku/bin
     - /home/railseng/.rvm/gems/ruby-2.0.0-p643/bin
     - /home/railseng/.rvm/gems/ruby-2.0.0-p643@global/bin
     - /home/railseng/.rvm/rubies/ruby-2.0.0-p643/bin
     - /usr/local/sbin
     - /usr/local/bin
     - /usr/sbin
     - /usr/bin
     - /sbin
     - /bin
     - /usr/games
     - /usr/local/games
     - /home/railseng/.rvm/bin
     - /home/railseng/.rvm/bin
     - /home/railseng/.rvm/bin
     - /home/railseng/.rvm/bin