How do you get over an error that says your already have a newer version

I downloaded a sample app that uses rack 1.2.2. When I tried to run it, it said “You have already activated rack 1.4.1, but your Gemfile requires rack 1.2.2. ”

So clearly I already have what I require. But backup was not happy. When I did a  ’bundle show’ it showed that I have 1.2.2. So where was the 1.4.1 that was ‘activated’? And how could I get rid of this error?

In my case this is probably what happened. I installed rack 1.2.2. Then I installed rack 1.4.1 with sudo gem install rack. That puts rack in a different location that my regular user and bundle and rackup cannot see.

Simple solution: gem uninstall rack. Choose to remove 1.4.1. Now rackup runs fine.