Getting an NSInternalInconsistencyException Error!

I am getting the error:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+entityForName: could not locate an NSManagedObjectModel for entity name 'Exercise''

At the line: Exercise *exercise = (Exercise *)[NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];

(You can see my data model here: How is This Data Model?). Any ideas why?

   - (void)viewDidLoad
    {
        [super viewDidLoad];

        UIBarButtonItem *addButton = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(exerciseChooser)];
        self.navigationItem.rightBarButtonItem = addButton;
        [addButton release];

        //if (managedObjectContext == nil) 
        { 
            managedObjectContext = [(CurlAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 
        }

        NSFetchRequest *request = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Exercise" inManagedObjectContext:managedObjectContext];
        [request setEntity:entity];

        NSLog(@"After managedObjectContext: %@",  managedObjectContext);


        NSError *error = nil;
        NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
        if (mutableFetchResults == nil) {
            // Handle the error.
        }
        [mutableFetchResults release];
        [request release];
    }

    -(IBAc开发者_开发问答tion)exerciseChooser
    {
        RoutineExerciseChooserViewController *routineExerciseChooserViewController = [[[RoutineExerciseChooserViewController alloc] init] autorelease];

        [self.navigationController pushViewController:routineExerciseChooserViewController animated:YES];
    }

    -(void)addExercise
    {    
        Exercise *exercise = (Exercise *)[NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];

        exercise.name=@"Test";

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

        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];

        NSInteger lastSection = [self.tableView numberOfSections] -1;

        [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:[self.tableView numberOfRowsInSection:lastSection]-1 inSection:lastSection] atScrollPosition:UITableViewScrollPositionBottom animated:YES];
    }

This error has only a few possible sources:

1. Typo in the Entity name.
2. Nil managed object context object.
3. Failure to add the model containing the entity to the persistent store the context uses.
4. Failure to add the correct persistent store to the context itself.

Please also refer to this previous question:

insertNewObjectForEntityForName:

UPDATE

Why is the if statement commented out?

if(managedObjectContext == nil) 

I think it's required.

EDIT

-(void)addExercise
{    
    if(managedObjectContext!=nil)
    {
        Exercise *exercise = (Exercise *)[NSEntityDescription insertNewObjectForEntityForName:@"Exercise" inManagedObjectContext:managedObjectContext];

        exercise.name=@"Test";

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

        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];

        NSInteger lastSection = [self.tableView numberOfSections] -1;

        [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:[self.tableView numberOfRowsInSection:lastSection]-1 inSection:lastSection] atScrollPosition:UITableViewScrollPositionBottom animated:YES];
    }
}