title: In eclipse, unable to reference an android library project in another android project
body: <p>As I was writing up this question I managed to solve it so repeat it here for the benefit of others. Here is the initial problem:</p>
  
  <p>I have created a very simple library project which I want to reference in another project. I have done this previously with no problems so not really sure why it is not working this time. I have:</p>
  
  <ol>
  <li><p>Flagged the library project via project properties. The <code>default.properties</code> file has this set : <code>android.library=true</code></p></li>
  <li><p>In my other project added reference to my library project via project properties. The <code>default.properties</code> file has the reference added as expected ie <code>android.library.reference.1=K:/android_test_ws/applicationRegistrar</code></p></li>
  <li><p>The green tick against the referenced library project starts off green and then changes to a red cross.</p></li>
  </ol>
  
  <p>This implies that there must be something wrong / missing from the library project but I don't know what. My library project on this occasion is MUCH simpler than the previous one I created.</p>