Sometimes, RMIDispatcher cannot be constructed

sometimes, the ofbiz instance startup failed because following error:

java.lang.NullPointerException
at javolution.util.FastMap$Entry.access$302(FastMap.java:1530)
at javolution.util.FastMap.put(FastMap.java:490)
at javolution.util.FastMap.put(FastMap.java:453)
at org.ofbiz.service.group.ServiceGroupReader.addGroupDefinitions(ServiceGroupReader.java:79)
at org.ofbiz.service.group.ServiceGroupReader.readConfig(ServiceGroupReader.java:62)
at org.ofbiz.service.ServiceDispatcher.<init>(ServiceDispatcher.java:104)
at org.ofbiz.service.ServiceDispatcher.<init>(ServiceDispatcher.java:151)
at org.ofbiz.service.ServiceDispatcher.getInstance(ServiceDispatcher.java:183)
at org.ofbiz.service.ServiceDispatcher.getLocalDispatcher(ServiceDispatcher.java:162)
at org.ofbiz.service.GenericDispatcherFactory.createLocalDispatcher(GenericDispatcherFactory.java:46)
at org.ofbiz.service.ServiceContainer.getLocalDispatcher(ServiceContainer.java:90)
at org.ofbiz.service.rmi.RmiServiceContainer.start(RmiServiceContainer.java:133)
at org.ofbiz.base.container.ContainerLoader.start(ContainerLoader.java:237)
at org.ofbiz.base.start.Start.startStartLoaders(Start.java:341)
at org.ofbiz.base.start.Start.start(Start.java:367)
at org.ofbiz.base.start.Start.main(Start.java:135)
20141110104822705 |Thread-0 |ContainerLoader |I| Shutting down containers
20141110104822705 |Thread-0 |ContainerLoader |I| Stopping container birt-container
20141110104822706 |Thread-0 |ContainerLoader |I| Stopped container birt-container
20141110104822706 |Thread-0 |ContainerLoader |I| Stopping container catalina-container
20141110104822706 |Thread-0 |ContainerLoader |I| Stopped container catalina-container
20141110104822706 |Thread-0 |ContainerLoader |I| Stopping container rmi-dispatcher
java.lang.NullPointerException
at org.ofbiz.service.rmi.RmiServiceContainer.stop(RmiServiceContainer.java:176)
at org.ofbiz.base.container.ContainerLoader.unload(ContainerLoader.java:264)
at org.ofbiz.base.start.Start.shutdownServer(Start.java:317)
at org.ofbiz.base.start.Start$1.run(Start.java:231)

Since it's hard to reproduce, and I'm not familiar with the logic behind it, I'm unable to figure out what the root cause is.

Anyone can help?