Building a universal app for iOS 3.1, iOS 3.2 using iOS SDK 4.2

I have a universal app which was originally built for iOS4.2. Since this project does not use many 4.0+ specific APIs, I would like to build this app with deployment target set to 3.1.

It gets built with no problems.

But when I install and start the app on the iPhone 3.1.3 simulator, I get the following dyld error:

Dyld Error Message:
Symbol not found: _OBJC_CLASS_$_UIActionSheet

iPad specific part of my code is already employs checks to make sure that it doesn't reference any unavailable symbols using:

        Class cls = NSClassFromString(@"UIPopoverController");
        if (cls != nil) {
            _popOverController = [[cls alloc] initWithContentVi开发者_如何学编程ewController:_settingsController];
        }

Any ideas?