The warning is pretty clear. You are trying to present a modal view by a view that is not in the window hierarchy, which won't work.
Try changing this [appDelegate.navController presentViewController:viewController animated:YES completion:nil];
to something like this instead:
[appDelegate.window.rootViewController presentViewController:viewController animated:YES completion:nil];
This guarantees that the currently active root view controller of your app will be the one presenting the modal view controller.
Depending on how your AppDelegate is built you may need to add a property or just a getter to surface the window
variable to the outside world.