title: Xcode compiles my App, but can't run it in the simulator
body: <p>when i compile my app, Xcode just says "Attaching to Projectname..." and gets stuck there.
  The debugger just prints this out:</p>
  
  <blockquote>
    <p>error: failed to attach to process ID 0</p>
  </blockquote>
  
  <p>I tried to clean &amp; build again and it still doesn't work out. I googled but couldn't find anything helpful.
  How can I fix this problem? Thank You!</p>