title: Project is missing required library - but correct JAR exists?
body: <p>One of my eclipse projects gives me the <code>Project X is missing required library: 'somelib.jar'</code> error, but when I go to <strong>Configure Build Path > Libraries</strong> the library <em>is</em> present, and no error is indicated there. </p>
  
  <p>I tried the usual things:</p>
  
  <ul>
  <li>Clean build (all projects in the workspace)</li>
  <li>Exited eclipse multiple times</li>
  </ul>
  
  <p>My coworkers, using the same git checkout with the same status as mine, and also using eclipse Neon2, have no build errors.</p>
  
  <p>Just to be sure, I navigated into the corresponding directory and removed a <em>different</em> jar file, and when I look at my build path configuration <em>that</em> jar shows up with a red "x" indicating that the library is missing.</p>
  
  <p>I checked that <code>somelib.jar</code> sits in the expected place and is a valid JAR file.</p>
  
  <p>How do I fix this?</p>