java - StatefulPersistenceContext: NullPointerException in hibernate library -

i have application running in tomcat 7.0.37 2 years without error yesterday gave one:

exception in thread "datamanager-general-info" java.lang.nullpointerexception @ org.hibernate.engine.statefulpersistencecontext.clear(statefulpersistencecontext.java:217) @ org.hibernate.impl.sessionimpl.cleanup(sessionimpl.java:623) @ org.hibernate.impl.sessionimpl.close(sessionimpl.java:351) @ org.hibernate.ejb.entitymanagerimpl.close(entitymanagerimpl.java:151) @ com.xxxxxxxxxx.datamanager$generalinfo.buildpages(datamanager.java:358) 

the error starts in class datamanager in line, when closing entitymanager:

entitymanager em  = null; try {     em = jpautil.getentitymanagerfactory().createentitymanager();      // code here...  } catch (exception e) {     // nothing } {     if (em != null && em.isopen()) {         em.close(); <-- line 358     } } 

now, repeating every 2-3 hours.

i'm using hibernate 3.6.10 jpa 2.0 api 1.0.1 , c3p0.

any welcome!