Why does the App Store think Xcode 4.2 is installed? I'm trying to upgrade Xcode from 4.1 to 4.2. 
However App Store thinks that it's already up to date, which it is not.




I am a registered Mac and iOS developer. I don't think 4.2 is under NDA. 

How can I fix this?
Delete the XCode installer in /Applications, restart App Store. Now you will have an "Install" button for XCode. Download the installer and run it.