iOS os 3.1.3 problem to run app

[MACloop]

Hello,
I have an app where built for iPhone iOS4, with iPhone OS Deployment Target to iPhone OS 3.0
When building the binaries I got no errors. Now when the app has been released on app store, users with 3.1.3 have problem to run the app. They say the app crashed on startup. So my problems are:
I cannot test for 3.1.3 because I have an iPhone 4 with iOS4 on it. Is there a way to test this?

The app delegate is compsed as it is as default for ios4 apps. It has the delegate methods for multitasking. Is this a problem maybe? I did n ot think so becaus I expected the Xcode to give me a hint if the app design would not work on 3.0, because the iPhone OS Deployment Target was set to iPhone OS 3.0...

Has anyone had the same issues? Does anyone have any advice on how to avoid backward compbility problems?
Thanks in advance!
MACloop

 

[PhoneyDeveloper]

You can only really test this with a device that has 3.1.3 installed.

If you don't have one then you should probably not release software for that OS version.

If you really really want to release for 3.1.3 then try to get the crash log from someone who has 3.1.3.

If the app crashes on launch then most likely you are using a class or constant that isn't available on 3.1.3 and you're doing this in a way that isn't backwards compatible.