SIGABRT when launching app with CoreData on iPhone 3.1.3

I am using CoreData on my iPhone app. When I test the app on a old 1g iPhone running iOS 3.1.3 I get a SIGABRT in this method

#pragma mark - Application's Documents directory

/**
 Returns the URL to the application's Documents directory.
 */
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

*** -[NSFileManager URLsForDirectory:inDomains:]: unrecognized selector sent to instance 0x106920
2011-04-08 23:49:26.311 TestApp[963:207] *** Te开发者_如何学Gorminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSFileManager URLsForDirectory:inDomains:]: unrecognized selector sent to instance 0x106920'
2011-04-08 23:49:26.321 TestApp[963:207] Stack:...

I am using XCode 4. It seems like the selector is not supported, however I thought they were saying that CoreData should work on iOS > 3.....so why are does the code that is generated along with it not working...

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URLsForDirectory is only available in iOS 4.0 and later

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Because the code is NOT related to Core Data but to an Foundation method on the NSFileManager class which is available since iOS 4.0.