Runtime shutdown hook called, forceHalt: true

Jboss randomly shuts itself down. The application server logs that a Runtime shutdown hook has been called. Often it happens that the AS goes up and then, after 1-2 minutes, it starts to shut itself down. This is not the rule, though. Sometimes, the server shutdowns in the middle of the day.

I manage about 100 JBAS and every other day one goes down with no reason. This is a severe problem as this behaviour is really bad in HA enviroments or when critical applications are deployed in JBoss (unfortunately this is my case).

In teh forum you can find a couple of threads with people that are having my same issue, like:
http://www.jboss.com/index.html?module=bb&op=viewtopic&t=79753
http://www.jboss.com/index.html?module=bb&op=viewtopic&t=82692

I attach the log of the AS

09:45:38,927 INFO [Server] Runtime shutdown hook called, forceHalt: true
09:45:38,927 INFO [Server] JBoss SHUTDOWN: Undeploying all packages
09:45:38,929 INFO [TomcatDeployer] undeploy, ctxPath=/jmx-console, warUrl=.../d
eploy/jmx-console.war/
09:45:39,001 INFO [TomcatDeployer] undeploy, ctxPath=/wslegaldoc, warUrl=.../tm
p/deploy/tmp62235xapdws.war/
09:45:39,037 INFO [TomcatDeployer] undeploy, ctxPath=/xapd, warUrl=.../tmp/depl
oy/tmp62234xapd.war/
09:45:39,372 INFO [STDOUT] xapd - Chiusura connessione 2006-05-18 09:45:39.0
09:45:39,404 INFO [TomcatDeployer] undeploy, ctxPath=/mnse.fw, warUrl=.../tmp/d
eploy/tmp62233mnse.fw.war/
09:45:39,465 INFO [TomcatDeployer] undeploy, ctxPath=/midcadmin, warUrl=.../app
s/midcadmin.war/
09:45:39,502 INFO [ConnectionFactoryBindingService] Unbound ConnectionManager '
jboss.jca:service=DataSourceBinding,name=DefaultDS' from JNDI name 'java:Default
DS'
09:45:39,693 INFO [HypersonicDatabase] Database standalone closed clean
09:45:39,730 INFO [ConnectionFactoryBindingService] Unbound ConnectionManager '
jboss.jca:service=DataSourceBinding,name=PostgresDSXAC' from JNDI name 'java:Pos
tgresDSXAC'
09:45:39,768 INFO [ConnectionFactoryBindingService] Unbound ConnectionManager '
jboss.jca:service=DataSourceBinding,name=PostgresDS' from JNDI name 'java:Postgr
esDS'
09:45:39,808 INFO [ConnectionFactoryBindingService] Unbound ConnectionManager '
jboss.jca:service=DataSourceBinding,name=OracleDS' from JNDI name 'java:OracleDS
'
09:45:39,898 INFO [MailService] Mail service 'java:/Mail' removed from JNDI
09:45:39,915 INFO [TomcatDeployer] undeploy, ctxPath=/web-console, warUrl=.../d
eploy/management/console-mgr.sar/web-console.war/
09:45:40,065 INFO [TomcatDeployer] undeploy, ctxPath=/, warUrl=.../deploy/jboss
web-tomcat55.sar/ROOT.war/
09:45:40,104 INFO [Http11Protocol] Pausing Coyote HTTP/1.1 on http-xapdsv.intra
.infocamere.it%2F1.5.29.74-8080
09:45:41,112 INFO [StandardService] Stopping service jboss.web
09:45:41,158 INFO [Http11Protocol] Stopping Coyote HTTP/1.1 on http-xapdsv.intr
a.infocamere.it%2F1.5.29.74-8080
09:45:41,166 INFO [TomcatDeployer] undeploy, ctxPath=/invoker, warUrl=.../deplo
y/http-invoker.sar/invoker.war/
09:45:41,170 INFO [TomcatDeployer] undeploy, ctxPath=/ws4ee, warUrl=.../tmp/dep
loy/tmp62184jboss-ws4ee.war/
Shutting down
09:45:41,544 INFO [Server] Shutdown complete
Shutdown complete
Halting VM