title: Ruby on Rails: gem not found even though it is installed
body: <p>I get this error trying to run any Ultrasphinx rake commands (under Linux terminal) such as rake ultrasphinx:configure : </p>
  
  <pre>
  rake aborted!
  no such file to load -- echoe
  /var/www/gitorious/vendor/plugins/ultrasphinx/Rakefile:2:in `require'
  /var/www/gitorious/vendor/plugins/ultrasphinx/Rakefile:2
  /usr/lib/ruby/1.8/rake.rb:2359:in `load'
  /usr/lib/ruby/1.8/rake.rb:2359:in `raw_load_rakefile'
  /usr/lib/ruby/1.8/rake.rb:1993:in `load_rakefile'
  /usr/lib/ruby/1.8/rake.rb:2044:in `standard_exception_handling'
  /usr/lib/ruby/1.8/rake.rb:1992:in `load_rakefile'
  /usr/lib/ruby/1.8/rake.rb:1976:in `run'
  /usr/lib/ruby/1.8/rake.rb:2044:in `standard_exception_handling'
  /usr/lib/ruby/1.8/rake.rb:1974:in `run'
  /usr/bin/rake:28
  </pre>
  
  <p>I gather this means echoe gem is not installed. But if I run "gem list --local" it shows that the echoe gem is installed. What could be the problem here and how can I debug this?</p>