title: gem and/or Ruby on Rails broke all of a sudden, anyone know what happened?
body: <p>I had a Ruby on Rails app that used to work.  I hadn't used it in a month or so, but then tried starting it up today with <code>rails s</code> and got the following error—in fact, I get this error when I try <code>rails -h</code> or <code>rails -v</code> or even <code>gem -h</code> or <code>sudo gem update --system</code> or anything having to do with <code>gem</code>.</p>
  
  <pre><code>NOTE: Gem::Specification#default_executable= is deprecated with no replacement. It will be removed on or after 2011-10-01.
  Gem::Specification#default_executable= called from /Library/Ruby/Gems/1.8/specifications/rubygems-update-1.8.2.gemspec:11.
  Invalid gemspec in [/Library/Ruby/Gems/1.8/specifications/tilt-1.3.3.gemspec]: invalid date format in specification: "2011-08-25 00:00:00.000000000Z"
  NOTE: Gem::Specification#default_executable= is deprecated with no replacement. It will be removed on or after 2011-10-01.
  Gem::Specification#default_executable= called from /Users/me/.gem/ruby/1.8/specifications/json-1.5.1.gemspec:10.
  /Library/Ruby/Site/1.8/rubygems/specification.rb:277:in `_resort!': undefined method `name' for nil:NilClass (NoMethodError)
      from /Library/Ruby/Site/1.8/rubygems/specification.rb:276:in `sort!'
      from /Library/Ruby/Site/1.8/rubygems/specification.rb:276:in `_resort!'
      from /Library/Ruby/Site/1.8/rubygems/specification.rb:270:in `_all'
      from /Library/Ruby/Site/1.8/rubygems/specification.rb:402:in `each'
      from /Library/Ruby/Site/1.8/rubygems/dependency.rb:216:in `find_all'
      from /Library/Ruby/Site/1.8/rubygems/dependency.rb:216:in `matching_specs'
      from /Library/Ruby/Site/1.8/rubygems/dependency.rb:238:in `to_specs'
      from /Library/Ruby/Site/1.8/rubygems/dependency.rb:256:in `to_spec'
      from /Library/Ruby/Site/1.8/rubygems.rb:1182:in `gem'
      from /usr/bin/rails:18
  </code></pre>
  
  <p>Anyone know what's going on and how to fix it? How can I uninstall it all and reinstall it (without uninstalling my OS, man that would really suck)</p>