I keep on getting "save operation failure" after any change on my XCode Data Model

I started using Core Data for iPhone development. I started out by creating a very simple entity (called Evaluation) with just one string property (called evaluationTopic). I had following code for inserting a fresh string:

- (void)insertNewObject {

    // Create a new instance of the entity managed by the fetched results controller.
    NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
    NSEntityDescription *entity = [[fetchedResultsController fetchRequest] entity];
    NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];

    // If appropriate, configure the new managed object.
    [newManagedObject setValue:@"My Repeating String" forKey:@"evaluationTopic"];

    // Save the context.
    NSError *error;
    if (![context save:&error]) {
        // Handle the error...
    }

    [self.tableView reloadData];

}

This worked perfectly fine and by pushing the +button a new “My Repeating String” would be added to the table view and be in persistent store.

I then pressed “Design -> Add Model Version” in XCode. I added three entities to the existing entity and also added new properties to the existing “Evaluation” entity. Then, I created new files off the entities by pressing “File -> New File -> Managed Object Classes” and created a new .h and .m file for my four entities, including the “Evaluation” entity with Evaluation.h and Evaluation.m. Now I changed the model version by setting “Design -> Data Model -> Set Current Version”. After having done all this, I changed my insertMethod:

- (void)insertNewObject {

    // Create a new instance of the entity managed by the fetched results controller.
    NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
    NSEntityDescription *entity = [[fetchedResultsController fetchRequest] entity];
    Evaluation *evaluation = (Evaluation *) [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];

    // If appropriate, configure the new managed object.
    [evaluation setValue:@"My even new string" forKey:@"evaluationSpeechTopic"];

    // Save the context.
    NSError *error;
    if (![context save:&error]) {
        // Handle the error...
    }

    [self.tableView reloadData];

}

This does not work though! Every time I want to add a row the simulator crashes and I get the following:

"NSInternalInconsistencyException', reason: 'This NSPersistentStoreCoordinator has no persistent stores.  It cannot perform a save operation.'"

I had this error before I knew about creating new version after changing anything on the datamodel, but why is this still coming up? Do I need to do any mapping (even though I just added entities and properties that did not exist before?). In the Apple Dev tutorial it sounds very easy but I have been struggling with this for long time, never worked after changing model version.

I keep on getting "save operation failure" after any change on my XCode Data Model