Get Ruby on Rails working on Ubuntu 11.10

A long time I have not been using Ruby On Rails. I have decided to give it a try again, so started by installing on Ubuntu 11.10 in VirtualBox. From what I remember - I have never happened before having issue with RoR working out of the box. Unfortunately this was not the case this time. Everything started with something really new to me: Invalid gemspec in [/var/lib/gems/1.8/specifications/json-1.6.1.gemspec]: invalid date format in specification: "2011-09-18 00:00:00.