Si ho trovato questa soluzione
Click on your target (the root of your project) then Build Settings > Deployment > iOS Deployment Target... which will show 4.3 and up.
You probably did the same, but went to General > Deployment Info > Deployment Target... which by default only goes to 6 until you reset it as shown above.
Also, if necessary, download the iOS 5 simulators needed to test your project.
mi chiedevo se volessi rendere comapatibile con ios 4 devo sviluppare la app con MRC e non so cosa fare per essere compatibile com ARC ma credo che non ne vale la pena la compatibilita con ios 4, no?