'Tried to pop to a view controller that doesn't exist.'

The -popToViewController is used to pop view controllers OFF the stack, down to one that already exists. Your UINavigationController has a stack of ViewControllers (stored in the viewControllers property), when you popToViewController, you're going to want to pass one of the elements in that array as the first argument.

What you most likely want to do in this case is use -popViewControllerAnimated:, which will remove the top ViewController from the stack

 [self.navigationController popViewControllerAnimated:YES];
    

You're allocating the RootViewController right there. It does not exist in the navigation controller's stack, so no matter how far you pop, you won't reach it.

 id viewController = [[RootViewController alloc] init];
    
    // ...

    [self.navigationController pushViewController:viewController animated:YES];
   // ...
    
    // Here is the initial view controller, not in the stack.
    [self.navigationController popToViewController:viewController animated:YES];
    

I had this problem recently and solved with something like this...

[self.navigationController popToViewController:[self.navigationController.viewControllers objectAtIndex:1] animated:YES];
    

If you are using Storyboads, use this segue:

@implementation PopToControllerSegue

- (void) perform
{
    UIViewController *sourceViewController = (UIViewController *)self.sourceViewController;
    UIViewController *destinationViewController = (UIViewController *)self.destinationViewController;

    for (UIViewController* controller in sourceViewController.navigationController.viewControllers) {
        if ([controller isKindOfClass:destinationViewController.class]) {
            [sourceViewController.navigationController popToViewController:controller animated:YES];
            return;
        }
    }

    NSLog(@"PopToControllerSegue has failed!");
}

@end
    

When using Push Segues you can easily go back to the root using this method:

[self.navigationController popToRootViewControllerAnimated:YES];
    

When using Modal Segues (because of the word dismiss in the question and as a general reference) you can dismiss the view controller using this method:

[self dismissViewControllerAnimated:YES completion:nil];
    

The UINavigationController has a stack of ViewControllers which is stored in the viewControllers(NSArray) property. Enumerate to the required ViewController and pop to that ViewController.

Following code should solve the problem.

-(IBAction)dismissView
{
    NSArray *array = self.navigationController.viewControllers;
    for (id controller in array) {
        if ([controller isKindOfClass:[RootViewController class]]) {
            [self.navigationController popToViewController:controller animated:YES];

        }
    }
}
    

Try this one line solution.

Swift 4+:

self.navigationController?.popToViewController ((self.navigationController?.viewControllers[1]) as! Your_ViewController, animated: true)
    

Objective-C:

[self.navigationController popToViewController:[self.navigationController.viewControllers objectAtIndex:1] animated:YES];
    

Swift 4

For anyone still looking for a better solution that doesn't involve the UINavigationController stack indexes, which is getting more problematic with bigger navigation stack - here's the easiest way to solve this:

if let destinationViewController = navigationController?.viewControllers
                                                        .filter(
                                      {$0 is DestinationViewController})
                                                        .first {
    navigationController?.popToViewController(destinationViewController, animated: true)
}
    

In my case the problem was that I was in the root ViewController and this works only for VCs that are stacked over it. To pop to the RootViewController use

navigationController?.popToRootViewController(animated: true)
    

self.navigationController?.present(viewControllers, animated: true, completion: nil)
    

Before popToViewController, check that NavigationController contains your ViewController:

if !navigationController.viewControllers.filter({ $0 == viewController}).isEmpty {
    navigationController.popToViewController(viewController, animated: true)
}