title: how to fix Eclipse losing reference to third party jar in project sets
body: <p>Occasionally I see eclipse lose the reference to the third party jars contained in the a projects. (you get the the build path error stating the jar cannot be found)</p>
  
  <p>Its easy enough to fix as you can remove the jar, save the properties of the project and then go in and re-add the jar that it could not find, eclipse can then see the path to the jar and you can then compile again.</p>
  
  <p>the problem is that if you have a lot of projects in your build you would have to do this task a lot.</p>
  
  <p>Is there anything you can do to force eclipse to recognise that it actually has the jar on its classpath?</p>