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

Check that "Use Standard System Header Directory Searching" (under "Build Settings") is set to Yes.

I accidentally changed that setting and had the same issue also.