Been having my first crack at Core Data and I'm getting the following error when running my code on my device, but it works fine on the simulator..

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

Some of my methods that might be causing the problem:

    - (NSManagedObjectContext *)managedObjectContext
{
    if (__managedObjectContext != nil)
    {
        return __managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil)
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init];
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return __managedObjectContext;
}

/**
 Returns the managed object model for the application.
 If the model doesn't already exist, it is created from the application's model.
 */
- (NSManagedObjectModel *)managedObjectModel
{
    if (__managedObjectModel != nil)
    {
        return __managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"RugbyOnTv" withExtension:@"momd"];
    __managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];    
    return __managedObjectModel;
}

/**
 Returns the persistent store coordinator for the application.
 If the coordinator doesn't already exist, it is created and the application's store added to it.
 */
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil)
    {
        return __persistentStoreCoordinator;
    }

    NSString *storePath = [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"RugbyOnTV.sqlite"];

    NSURL *storeUrl = [NSURL fileURLWithPath:storePath];

    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];    
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];

    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];


    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:options error:&error]) {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}


    - (NSString *)applicationDocumentsDirectory {

        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
        return basePath;
    }

EDIT

I copied and pasted the managedObjectContext method (below) from Apple's CoreDataBooks and it now works..Not really sure why though

- (NSManagedObjectModel *)managedObjectModel {
    if (managedObjectModel != nil) {
        return managedObjectModel;
    }
    managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];    
    return managedObjectModel;
}