rbx-head error with gem

rbx-head-gem

% gem
An exception occurred running /home/lamnk/.rvm/rubies/rbx-head/lib/bin/gem.rb
    Missing or uninitialized constant: Psych::Parser (NameError)

Backtrace:
                  Module#const_missing at kernel/common/module.rb:468
 Psych::Nodes::Stream.__class_init__ (Stream) at .rvm/rubies/rbx-head/lib/19
                                                 /psych/nodes/stream.rb:12
 Psych::Nodes.__module_init__ (Nodes) at .rvm/rubies/rbx-head/lib/19/psych/nodes
                                         /stream.rb:7
        Psych.__module_init__ (Psych) at .rvm/rubies/rbx-head/lib/19/psych/nodes
                                         /stream.rb:2
                    Object#__script__ at .rvm/rubies/rbx-head/lib/19/psych/nodes
                                         /stream.rb:1
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:207
  Kernel(Object)#gem_original_require (require) at kernel/common/kernel.rb:631
               Kernel(Object)#require at .rvm/rubies/rbx-head/lib/rubygems
                                         /custom_require.rb:36
                    Object#__script__ at .rvm/rubies/rbx-head/lib/19/psych
                                         /nodes.rb:2
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:207
  Kernel(Object)#gem_original_require (require) at kernel/common/kernel.rb:631
               Kernel(Object)#require at .rvm/rubies/rbx-head/lib/rubygems
                                         /custom_require.rb:36
                    Object#__script__ at .rvm/rubies/rbx-head/lib/19/psych.rb:2
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:207
  Kernel(Object)#gem_original_require (require) at kernel/common/kernel.rb:631
               Kernel(Object)#require at .rvm/rubies/rbx-head/lib/rubygems
                                         /custom_require.rb:36
                    Object#__script__ at .rvm/rubies/rbx-head/lib/19/yaml.rb:57
          Rubinius::CodeLoader.require at kernel/common/codeloader.rb:207
  Kernel(Module)#gem_original_require (require) at kernel/common/kernel.rb:631
               Kernel(Module)#require at .rvm/rubies/rbx-head/lib/rubygems
                                         /custom_require.rb:36
                        Gem.load_yaml at .rvm/rubies/rbx-head/lib
                                         /rubygems.rb:658
            Gem::ConfigFile#load_file at .rvm/rubies/rbx-head/lib/rubygems
                                         /config_file.rb:235
           Gem::ConfigFile#initialize at .rvm/rubies/rbx-head/lib/rubygems
                                         /config_file.rb:178
      Gem::GemRunner#do_configuration at .rvm/rubies/rbx-head/lib/rubygems
                                         /gem_runner.rb:78
                   Gem::GemRunner#run at .rvm/rubies/rbx-head/lib/rubygems
                                         /gem_runner.rb:51
                    Object#__script__ at .rvm/rubies/rbx-head/lib/bin/gem.rb:21
      Rubinius::CodeLoader#load_script at kernel/delta/codeloader.rb:67
      Rubinius::CodeLoader.load_script at kernel/delta/codeloader.rb:109
               Rubinius::Loader#script at kernel/loader.rb:631
                 Rubinius::Loader#main at kernel/loader.rb:835


apache3:~ % rvm info

rbx-head:

  system:
    uname:       "Linux apache3 2.6.18-274.7.1.el5.028stab095.1PAE #1 SMP Mon Oct 24 21:55:06 MSD 2011 i686 i686 i386 GNU/Linux"
    bash:        "/bin/bash => GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)"
    zsh:         "/bin/zsh => zsh 4.3.17 (i686-redhat-linux-gnu)"

  rvm:
    version:      "rvm 1.13.0 (stable) by Wayne E. Seguin <[email protected]>, Michal Papis <[email protected]> [https://rvm.io/]"
    updated:      "16 hours 41 minutes 15 seconds ago"

  ruby:
    interpreter:  "rubinius"
    version:      "2.0.0dev"
    date:         "rubinius 2.0.0dev (1.9.3 a0d398ac yyyy-mm-dd JI) [i686-pc-linux-gnu]"
    platform:     "i686-pc-linux-gnu"
    patchlevel:   "1.9.3 a0d398ac yyyy-mm-dd JI"
    full_version: "rubinius 2.0.0dev (1.9.3 a0d398ac yyyy-mm-dd JI) [i686-pc-linux-gnu]"

  homes:
    gem:          "/home/lamnk/.rvm/gems/rbx-head"
    ruby:         "/home/lamnk/.rvm/rubies/rbx-head"

  binaries:
    ruby:         "/home/lamnk/.rvm/rubies/rbx-head/bin/ruby"
    irb:          "/home/lamnk/.rvm/rubies/rbx-head/bin/irb"
    gem:          "/home/lamnk/.rvm/rubies/rbx-head/bin/gem"
    rake:         "/home/lamnk/.rvm/rubies/rbx-head/bin/rake"

  environment:
    PATH:         "/home/lamnk/.rvm/gems/rbx-head/bin:/home/lamnk/.rvm/gems/rbx-head@global/bin:/home/lamnk/.rvm/rubies/rbx-head/bin:/home/lamnk/.rvm/bin:/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/home/lamnk/bin"
    GEM_HOME:     "/home/lamnk/.rvm/gems/rbx-head"
    GEM_PATH:     "/home/lamnk/.rvm/gems/rbx-head:/home/lamnk/.rvm/gems/rbx-head@global"
    MY_RUBY_HOME: "/home/lamnk/.rvm/rubies/rbx-head"
    IRBRC:        "/home/lamnk/.rvm/rubies/rbx-head/.irbrc"
    RUBYOPT:      ""
    gemset:       ""