Thy this link. You have to set your application to support all orientations at the start. Do the change in app delegate.
-(NSUInteger)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window
{
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
return UIInterfaceOrientationMaskAll;
else /* iphone */
return UIInterfaceOrientationMaskAllButUpsideDown;
}