iOS App Store Package (.ipa) option got disabled after archive

This happens when your build produces more than a single target: say, an app and a library....

Credit:
http://stackoverflow.com/questions/5265292/xcode-4-create-ipa-file-instead-of-xcarchive

Related:
http://iphonedevelopertips.com/xcode/distribute-ad-hoc-applications-over-the-air-ota.html