Coredata Exception in iphone

I have created Core data app. It was working fine now it is giving exception

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Cannot create an 开发者_StackOverflow NSPersistentStoreCoordinator with a nil model'

Whats the problem?

It can't find the generated .mom or .momd file. I would recommend deleting the instance of the app on the iPhone or iPhone simulator and re-running. You don't happen to have separate programs that rely on one Core Data model, do you?