Availability.h, UIKit.h, etc not found

Question

I\'m having a great problem here.

I recently downloaded Xcode 4.3 from the Mac App Store, because it had the full-screen feature for Lion. And then, my project stopp

Answer 1

I experienced the same problem after I cloned my old computer to new one with the migration assistant.

I solved it simply by deleting content of DerivedData folder (/Users/userName/Library/Developer/Xcode/DerivedData).

I guess clean uninstall or installing new version of xCode does the same.