title: Issue with frameworks header in my project
body: <p>I updated Xcode to the 4.3.1 version but now I don't know what's going on. When I compile my project, the compiler gives this error:</p>
  
  <blockquote>
    <p>Lexical issue : 'Availability.h' file not found</p>
  </blockquote>
  
  <p>And in other old projects :</p>
  
  <blockquote>
    <p>Lexical issue'QuartzCore/QuartzCore.h' file not found</p>
  </blockquote>
  
  <p>It's so strange! But how can I fix these errors?</p>
  
  <p>I already removed frameworks and added them again, but nothing changed.</p>
  
  <p><img src="https://i.stack.imgur.com/XijzK.png" alt="enter image description here"></p>