Hi!

There are two things that limit on which iOS version an app can be started.

First: The Info.plist file contains a minimum system version. If this is set to 5.1, it will only run on 5.1

Second: If the app uses library calls which are only present in iOS 5.1, the app will not run/crash on earlier systems if the info.plist minimum version is below 5.1.

If the app you have to refactor was written using the Xcode 3 IDE, it is not possible that it will only run on iOS 5.1 since there is no iOS 5.1 SDK for Xcode 3.

Hope that helps!