The "Object's persistent store is not reachable from this NSManagedObjectContext's coordinator"
This message means you tried to use a managed object that was loaded from the data store that you just removed. You removed the persistent store from the coordinator and deleted the store file, but you still have at least one NSManagedObject
that you loaded from that store. You can't use those objects any more, because if you do, you get this specific exception. Make sure you get rid of any existing managed objects before going nuclear on the Core Data stack in your second snippet.
As for why this works in a different app, most likely that app isn't holding on to stale managed objects.