Your site needs the bundle install

From shell, you will need to run the bundle command:

( Command: bundle install )

You will get asked for your root password. Simply enter your password. The password request can be disabled, but this take a custom configuration. If you would like to bypass the password, you can run the bundle install with the deployment command.:

That should be it. If your site is still showing an error most likely you are missing a specific Gem.