title: Unable to resolve target 'android-21'
body: <p>I have the latest ADT plugin for eclipse: <strong>ADT-23.0.4</strong>.<br>
  Eclipse Version: <strong>Luna Service Release 1 (4.4.1)</strong>.</p>
  
  <p>Still I am getting this error while importing a project: </p>
  
  <blockquote>
    <p><em>Unable to resolve target 'android-21'</em> </p>
  </blockquote>