I am presenting a modal view controller from another modal view controller, and this worked fine under all iOS versions prior to iOS6. But under iOS6 I am getting the following warning message in the emulator: Warning: Attempt to present <UINavigationController: 0x14e93680> on <UINavigationController: 0x9fc6b70> while a presentation is in progress! The modal view controller is not shown if this warning appears. Basically I am using code like this to show the modal view controller: WebAuthViewController *authController = [[WebAuthViewController alloc] initWithNibName:nil bundle:nil]; authController.challenge = challenge; authController.delegate = self; UINavigationController *aNavController = [[UINavigationController alloc] initWithRootViewController:authController]; [self presentModalViewController:aNavController animated:YES]; [aNavController release]; [authController release]; The view that is already shown is a UIWebView also shown in a modal view, like this: WebViewController *addController = [[WebViewController alloc] initWithNibName:nil bundle:nil]; addController.urlToLoad = [NSURL URLWithString:urlString]; addController.delegate = self; UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:addController]; navigationController.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal; [self presentModalViewController:navigationController animated:YES]; [navigationController release]; [addController release]; The apple docs still suggest that one is supposed to be able to stack navigation controllers like this, so I am at a loss to explain why this happens. Any hints?