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

Ivan's answer

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

For me the "Use Standard System Header Directory Searching" was already set to YES, however I ticked it to NO, then back to YES, and did both a Clean and a Clean Build Folder (Product -> Clean and (ALT) Product -> Clean Build Folder) which seemed to have solved the issue for me.

Now I'm not sure what steps in this process had actually fixed it (I had cleaned the build folder prior to this with no avail), but it worked.