title: My ipad app crashed after I modifed the xcdatamodel file
body: <p>I went in to myapp.xcdatamodel and added an attribute to an entity.  I then try to run my app and it dies at this line:</p>
  
  <pre><code>self.managedObjectContext = [delegate managedObjectContext];
  </code></pre>
  
  <p>do I need to do something special after saving the xcdatamodel file?</p>