java.lang.NoClassDefFoundError: javax/persistence/EntityManager

EJB is compiled , deployed, being called successfuly the first business method. When I use em I am getting this error. I even included javas.persistence.* replated jars to my project EAR.

imports

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

Em initiated

@PersistenceContext
private EntityManager em;

em refered

if (em.isOpen())
{
System.out.println("I am open");
}
else
{
System.out.println("I am not open");
}

thx
rrmr