fix error reporting on attempting to save content_block instances

Author: Andy Olliver

app/views/cms/application/_exception.html.erb

@@ -1,6 +1,6 @@
 <div class="errorExplanation" id="errorExplanation">
  <h2>An Error Occurred</h2>
  <ul>
- <li><%=h "#{exception.class.name}: #{exception.message}" %></li>
+ <li><%=h "#{@exception.class.name}: #{@exception.message}" %></li>
  </ul>
 </div>