Core Data NSInvalidArgumentException Error

I am getting a crash when changing a BOOL attribute of my NSManagedObject.

The code to save the object is:

self.detailItem.bookmark = [NSNumber numberWithBool:YES];
NSError *error = nil;
if (!    [self.detailItem.managedObjectContext save:&error]) 
{
    // Handle the error.
}
NSLog(@"%@", error);

And the error:

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.'