title: can't modify frozen Hash in rails3
body: <p>I'm getting the following error,</p>
  
  <pre><code>can't modify frozen Hash
  /home/.rvm/gems/ruby-1.9.3-p327@ui/gems/activerecord-3.2.6/lib/active_r
  ecord/attribute_methods/write.rb:38:in `[]='
  /home/.rvm/gems/ruby-1.9.3-p327@ui/gems/activerecord-3.2.6/lib/active_r
  ecord/attribute_methods/write.rb:38:in `write_attribute'
  </code></pre>
  
  <p>from this line</p>
  
  <pre><code>write_attribute(:value, new_value)
  </code></pre>
  
  <p>This can be run properly for certain days. But, now it fail continously with an above error. I tried out solution for that but nothing work for me.</p>