mocha gem error on dreamhost

I've just signed up to dreamhost and I'm trying to set up a rails
application but I get a 'Rails application failed to start properly'
on the welcome screen of the rails page.
I followed the instructions on the wiki page on how to set up your
rails app on dreamhost.
when I enter: ./dispatch.fcgi
I receive the error: 'could not find Rubygem Mocha'

Anyone knows what this is about ?
Thanks alot.