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

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.