title: import javax.persistence.EntityManager error
body: <p>I have copied my project from pc to other and i got error</p>
  
  <ol>
  <li>import javax.persistence.EntityManager; 
  importjavax.persistence.EntityManagerFactory; import
  javax.persistence.Persistence; import javax.persistence.Query;</li>
  </ol>
  
  <p>the compiler doesn't know them, in the lib folder i added 3 jar from the local pc
  derby.jar eclipselink.jar and also javax.persistence_2.0.4.v201112161009.jar</p>
  
  <p>what could be the reason </p>