There was a recent change to the rubyzip gem that required a dependency lock on the iron_worker_ng gem.
to fix this update to the latest version by running the command.
gem update iron_worker_ng
Your gem version should be iron_worker_ng (1.0.2)
You can test this by running
iron_worker -v
It should look like iron_worker_ruby_ng-1.0.2 (iron_core_ruby-1.0.1) as of 09/12/13.