/active_support/dependencies.rb:55: uninitialized constant ActiveSupport::Dependencies::Mutex (NameE

root@ubuntu10:~/up_zycg/up_zycg# ruby script/server
/usr/local/rvm/gems/ruby-1.8.7-p352/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:55: uninitialized constant ActiveSupport::Dependencies::Mutex (NameError)
    from /usr/local/rvm/rubies/ruby-1.8.7-p352/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
    from /usr/local/rvm/rubies/ruby-1.8.7-p352/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
    from /usr/local/rvm/gems/ruby-1.8.7-p352/gems/activesupport-2.3.5/lib/active_support.rb:56
    from /usr/local/rvm/rubies/ruby-1.8.7-p352/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
    from /usr/local/rvm/rubies/ruby-1.8.7-p352/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
    from /usr/local/rvm/gems/ruby-1.8.7-p352/gems/rails-2.3.5/lib/commands/server.rb:1
    from /usr/local/rvm/rubies/ruby-1.8.7-p352/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
    from /usr/local/rvm/rubies/ruby-1.8.7-p352/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'
    from script/server:3

解决方法：

require 'thread'

to the top of config/boot.rb.