我正在尝试设置rails应用程序，但遇到以下错误。运行时
rake db:migrate --trace
un-defining :chars method on String for ruby 1.8.7
compatibility
rake aborted!
undefined method `cache' for Gem:Module
/usr/local/rvm/rubies/ruby-1.8.7-p371/lib/ruby/site_ruby/1.8/rubygems/core_ext/kernel_require.rb:55:in `gem_original_require'
/usr/local/rvm/rubies/ruby-1.8.7-p371/lib/ruby/site_ruby/1.8/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/rake_module.rb:25:in `load'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/rake_module.rb:25:in `load_rakefile'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:583:in `raw_load_rakefile'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:89:in `load_rakefile'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:160:in `standard_exception_handling'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:88:in `load_rakefile'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:72:in `run'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:160:in `standard_exception_handling'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/lib/rake/application.rb:70:in `run'
/usr/local/rvm/gems/ruby-1.8.7-p371@global/gems/rake-10.0.3/bin/rake:33
/usr/local/rvm/gems/ruby-1.8.7-p371@mapwalk/bin/rake:23:in `load'
/usr/local/rvm/gems/ruby-1.8.7-p371@mapwalk/bin/rake:23
/usr/local/rvm/gems/ruby-1.8.7-p371@mapwalk/bin/ruby_noexec_wrapper:14
ruby版本：1.8.7 rails版本：1.2.3 rubygems：1.4.2
宝石列表：
*** LOCAL GEMS ***
actionmailer (1.3.3)
actionpack (1.13.3)
actionwebservice (1.2.3)
activerecord (1.15.3)
activesupport (1.4.2)
bundler (1.2.3)
gem-wrappers (1.2.4)
rails (1.2.3)
rake (10.0.3, 0.9.2, 0.8.7)
rubygems-bundler (1.1.0)
rubygems-update (1.4.2)
rvm (1.11.3.5)
提前致谢..