Had an issue a while ago where running the capistrano deploy common would sorta run capistrano but always got the following error.
The deploy has failed with an error: No live threads left. Deadlock?
The quick and easy answer is to make sure to prefix the cap command with bundle exec. So it should look like
bundle exec cap production deploy
There is some strange behavior here that I have not found the cause of yet. Something about how bundler executes ruby scripts. So just a heads up.