iOS core data error: 'Can't do regex matching on object 0

[weny]

I'm creating a core data favorite feature. I have a favorite attribute with type boolean in recipe table. There are 2 views.

First view is for user to select favorite.
Second view display a list of favorites that is selected.

The feature works fine when i go to the first view. However, the app crashed after i go to the second view and go back to first view again. I get the following error:

  2012-01-09 18:44:09.455 coredata[1354:12503] CoreData: error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  Can't do regex matching on object 0. with userInfo (null)
    2012-01-09 18:44:09.457 coredata[1354:12503] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Can't do regex matching on object 0.'

My code for the method in first view that toggle the favorite attribute to 1 or 0:

    - (IBAction)favoriteButtonPressed:(id)sender {
        
     if (recipe.favorite == 0) {
    
     [favoriteButton setSelected:YES];
     favoriteButtonSelected = 1;
     [favoriteButtonImage setImage:[UIImage imageNamed:@"selected.png"] forState:UIControlStateNormal];
     
         self.recipe.favorite = [NSNumber numberWithInteger:1];
     
     }else {
     
     [favoriteButton setSelected:NO];
     favoriteButtonSelected = 0;
     [favoriteButtonImage setImage:[UIImage imageNamed:@"unselected.png"] forState:UIControlStateNormal];
     
         self.recipe.favorite = [NSNumber numberWithInteger:0];
    
     }
        NSManagedObjectContext *context = recipe.managedObjectContext;
        NSError *error;
     if (![context save:&error]) {
      NSLog(@"Tried to save favorite Unresolved error %@, %@", error, [error userInfo]);abort();
         }
    }

Is it a problem that i did not update the database? I have searched around and found the following method, where should i include this into the code?

[context refreshObject:recipe mergeChanges:NO];

Can anyone help please? Thanks!