I've just installed RubyMine (after having this same problem with IDEA Ruby plugin). I've configured my Ruby SDK, and used the GemManager to install two gems (httpclient and soap4j). The two gems are visible in the Project tree under "External Libraries", and I can navigate into the gem's source files using the ^B shortcut from my own source file, but when I try to execute my Ruby script from within IDEA/RubyMine I get this error:
/usr/lib/ruby/1.8/rubygems.rb:827: in 'report_activate_error' : Count not find RubyGem httpclient (>= 0) (Gem::LoadError)
What am I doing wrong? I'm using RubyMine 2.0.2 on Ubuntu 10.04.