Xcode 5 Couldn't build module Cocoa after installing Xcode 6 beta 2

Question

I just installed Xcode 6 beta 2. After trying it out, I wanted to continue my work and build a project (created with 5.1 and never opened in Xcode 6), in Xcode 5.1 but I get the

Answer 1

If you opened that project in Xcode 6, it's busted now. You need to revert it to before that. Hope you have SCM in place, or at least TimeMachine.

Otherwise, check what xcode-select -p says. You may have to re-select Xcode 5. Alternatively, open Xcode Preferences and select the last tab “Locations”. There is a pop-up menu for Command Line Tools. It may still point to Xcode 6.

Answer 2

I finally restored Xcode 5 using Time Machine to a version before my install of Xcode 6 Beta 2. It works again, but I have no idea what Xcode 6 Beta 2 did to break it.