App Crashes when iAds is integrated. What could be wrong?

I have integrated iAds in the app.

Simulator -> Works fine.

iPhone 3G (iOS 4.2.1) - Installed from XCode -> Works fine.

iPhone 4G (iOS 4.0.1) - Tried installing Adhoc -> App crashes after 2 seconds of opening.

I have tried deleting the provisioning profiles and reinstalling them.

What could be wrong开发者_Python百科?

Please suggest.

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Do you use ADBannerContentSizeIdentifierLandscape, ADBannerContentSizeIdentifierPortrait constants? Using them will crash on <4.2, use the old ADBannerContentSizeIdentifier480x32, ADBannerContentSizeIdentifier320x50 instead