JBoss: Unable to acquire lock on Fqn

We have some production JBoss 5.0.1.GA servers and from time to time we got this error

Caused by: org.jboss.cache.lock.TimeoutException: Unable to acquire lock on Fqn [/persistence.unit:unitName=z-eBF-ejb3Beans.jar#ebf-ejb3-beansUnit/ar/com/sdd/ebf/bo/do cument/DocumentBean/ENTITY/ar.com.sdd.ebf.bo.document.DocumentBean#55420546] after [25000] milliseconds for requestor [GlobalTransaction::420001]! Lock held by [ GlobalTransaction::406079]

We have two or three JBoss instances per Linux server, but not in a cluster. Just separated JBoss instances, each one with it's independent configuration and database.

We've been dealing with it since we开发者_Go百科 moved from JBoss 4 to JBoss 5, and we can't figure out how to solve the problem.

We just need some clues, or where in the documentation to look at.