Where are you registering for the notifications? You need to remove the observer when you are about to change orientations (either in prepForSegue or willAnimateRotationToInterfaceOrientation depending on however you've got your setup) in order prevent messaging a no longer valid object. You also don't want to pile up several notifications if your registering in viewDidAppear/viewWillAppear.
Remove the observer using:
[[NSNotificationCenter defaultCenter] removeObserver:self];//removes all notifications for that object (the way I've used it before)
or if you want to be specific, do something like:
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIDeviceOrientationDidChangeNotification object:[UIDevice currentDevice];//remove just that notification