Redmine

I've been going round looking at the install/help/forums and am stuck - please can someone point out my error.

This is my first usage of Ruby and only the second (after TestLink) of MySQL - so although I can use Linux, I have no confidence with 'make' or installation more complex than single click stuff.

RAILS_ENV=development script/about
/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:55: uninitialized constant ActiveSupport::Dependencies::Mutex (NameError)
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `require'
    from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support.rb:56
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `require'
    from /var/www/redmine/config/../vendor/plugins/engines/lib/engines.rb:1
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `require'
    from /var/www/redmine/config/../vendor/plugins/engines/boot.rb:8
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `require'
    from /var/www/redmine/config/environment.rb:15
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `require'
    from /usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/commands/about.rb:1
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:53:in `require'

Many thanks

Simon