Annotation @ElementCollection causes random Entity Error

On our project, if we add the annotation @ElementCollection on any Entity, eclipse got random errors on entities that not exists, because project runs without problem, if we remove the annotation @ElementCollection the errors disappear. Examples: On @Entity annotation the error is: "Name is Empty" On @ManyToMany the error is: "The attribute type for a collection mapping must be java.util.Collection, java.util.Set, java.util.List or java.util.Map"

Error Trace: !ENTRY org.eclipse.jpt.jpa.core 4 0 2013-11-18 15:22:19.310 !MESSAGE !STACK 0 java.lang.NullPointerException at org.eclipse.jpt.jpa.core.internal.context.java.AbstractJavaPersistentAttribute.getMappingKey(AbstractJavaPersistentAttribute.java:211) at org.eclipse.jpt.jpa.core.internal.jpa1.context.AbstractPersistentAttributeValidator.validate(AbstractPersistentAttributeValidator.java:33) at org.eclipse.jpt.jpa.core.internal.context.java.AbstractJavaPersistentAttribute.validateAttribute(AbstractJavaPersistentAttribute.java:645) at org.eclipse.jpt.jpa.core.internal.context.java.AbstractJavaPersistentAttribute.validate(AbstractJavaPersistentAttribute.java:640) at org.eclipse.jpt.jpa.core.internal.context.java.AbstractJavaPersistentType.validateAttribute(AbstractJavaPersistentType.java:903) at org.eclipse.jpt.jpa.core.internal.context.java.AbstractJavaPersistentType.validateAttributes(AbstractJavaPersistentType.java:897) at org.eclipse.jpt.jpa.core.internal.context.java.AbstractJavaPersistentType.validate(AbstractJavaPersistentType.java:883) at org.eclipse.jpt.jpa.core.internal.jpa1.context.persistence.GenericClassRef.validateJavaManagedType(GenericClassRef.java:444) at org.eclipse.jpt.jpa.core.internal.jpa1.context.persistence.GenericClassRef.validate(GenericClassRef.java:438) at org.eclipse.jpt.jpa.core.internal.context.persistence.AbstractPersistenceUnit.validateClassRefs(AbstractPersistenceUnit.java:2382) at org.eclipse.jpt.jpa.core.internal.context.persistence.AbstractPersistenceUnit.validate(AbstractPersistenceUnit.java:2264) at org.eclipse.jpt.jpa.core.internal.jpa1.context.persistence.GenericPersistence.validatePersistenceUnit(GenericPersistence.java:347) at org.eclipse.jpt.jpa.core.internal.jpa1.context.persistence.GenericPersistence.validate(GenericPersistence.java:303) at org.eclipse.jpt.jpa.core.internal.jpa1.context.persistence.GenericPersistenceXml.validate(GenericPersistenceXml.java:242) at org.eclipse.jpt.jpa.core.internal.jpa1.context.GenericContextModelRoot.validate(GenericContextModelRoot.java:248) at org.eclipse.jpt.jpa.core.internal.AbstractJpaProject.validate(AbstractJpaProject.java:1457) at org.jboss.tools.hibernate.jpt.core.internal.HibernateJpaProject.validate(HibernateJpaProject.java:289) at org.eclipse.jpt.jpa.core.internal.AbstractJpaProject.getValidationMessages(AbstractJpaProject.java:1445) at org.eclipse.jpt.jpa.core.internal.InternalJpaProjectManager.buildValidationMessages_(InternalJpaProjectManager.java:584) at org.eclipse.jpt.jpa.core.internal.InternalJpaProjectManager$BuildValidationMessagesCommand.execute(InternalJpaProjectManager.java:572) at org.eclipse.jpt.common.core.internal.utility.command.CommandJobCommandAdapter.execute(CommandJobCommandAdapter.java:50) at org.eclipse.jpt.common.core.internal.utility.command.JobCommandJob.run(JobCommandJob.java:42) at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)