title: Core Data NSInvalidArgumentException Error
body: <p>I am getting a crash when changing a BOOL attribute of my NSManagedObject.</p>
  
  <p>The code to save the object is:</p>
  
  <pre><code>self.detailItem.bookmark = [NSNumber numberWithBool:YES];
  NSError *error = nil;
  if (!    [self.detailItem.managedObjectContext save:&amp;error]) 
  {
      // Handle the error.
  }
  NSLog(@"%@", error);
  </code></pre>
  
  <p>And the error:</p>
  
  <pre><code>Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  The left hand side for an ALL or ANY operator must be either an NSArray or an NSSet. with userInfo (null)
  2011-08-18 15:41:32.866 Codes[5260:707] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'The left hand side for an ALL or ANY operator must be either an NSArray or an NSSet.'
  </code></pre>