You need to update Xcode to the latest version (4.2.1). Go to the App Store and find Xcode. If you already have 4.2, but it’s difficult for you to find how to upgrade to 4.2.1 or higher, after clicking “install” in the App Xcode App Store, go to Finder> Applications and launch the “Install XCode” application or install or upgrade.
Upon completion, go to the "About" menu in the Xcode menu bar and check to see the Xcode version again to make sure the update / installation was successful.
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