Simple problem with a simple solution. The new json_pure (1.4.3) makes older heroku gems explode.

Symptoms

$ heroku console
/Users/jdl/.rvm/rubies/ruby-1.8.7-p248/lib/ruby/site_ruby/1.8/rubygems.rb:233:in `activate': can’t activate json_pure (~> 1.2.0, runtime) for [“heroku-1.9.1”], already activated json_pure-1.4.3 for [“gemcutter-0.5.0”] (Gem::LoadError)

Gems involved in this collision

$ gem list —local | ack “(json_pure|heroku)”
heroku (1.9.1, 1.6.3)
json_pure (1.4.3, 1.2.4)

The solution

$ gem install heroku
Successfully installed heroku-1.9.11