Applications are expected to have a root view controller at the end of application launch

Replace in AppDelegate

 [window addSubview:[someController view]];


  [self.window setRootViewController:someController];

I had this same problem. Check your main.m. The last argument should be set to the name of the class that implements the UIApplicationDelegate protocol.

retVal = UIApplicationMain(argc, argv, nil, @"AppDelegate");

I had the same error when trying to change the first view controller that was loaded in

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

At first I didn't really know where the error was coming from precisely so I narrowed it down and found out what went wrong. It turns out that I was trying to change the display of a view before it actually came on screen. The solution was hence to move this code in the viewcontroller that was giving me trouble from

- (void)viewDidLoad


- (void)viewDidAppear:(BOOL)animated

and the error stopped appearing. My problem specifically was caused by making a UIAlertView show.

In your case I suggest you check out the code in the tabBarController's active view controller (as it is probably a problem in that view controller). If that doesn't work, try to set the starting settings in the nib file instead of in code - or if you want to do it in code, try moving the code to the tabBarController's active viewcontroller's appropriate method.

Good luck!