error 500

Hi,
 
From today we can't access to the home page of jahia ...(4.0.4 version)
We have an error 500.
Restarting Tomcat no resolve the pb.
We have in the log many errors, witch details is following :
 
"2005-03-29 16:05:33 StandardManager[/jahia] L''écouteur d''évènement de session (session event listener) a généré une exception
java.lang.IllegalStateException: "getAttributeNames": Session déjà invalidée
 at org.apache.catalina.session.StandardSession.getAttributeNames(StandardSession.java:974)
 at org.apache.catalina.session.StandardSessionFacade.getAttributeNames(StandardSessionFacade.java:181)
[...]
 
2005-03-29 16:09:18 ApplicationDispatcher[/jahia] Exception d'allocation pour la servlet Jahia
javax.servlet.ServletException: "Servlet.init()" pour la servlet Jahia a généré une exception
 at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:963)
 at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:668)
[...]
----- Root Cause -----
java.lang.NullPointerException
 at org.jahia.services.usermanager.JahiaGroupManagerRoutingService.init(JahiaGroupManagerRoutingService.java:158)
 at org.jahia.registries.ServicesRegistry.loadService(ServicesRegistry.java:651)
 at org.jahia.registries.ServicesRegistry.init(ServicesRegistry.java:308)
 at org.jahia.bin.Jahia.initServicesRegistry(Jahia.java:959)
 at org.jahia.bin.Jahia.init(Jahia.java:457)
[...]"
 
It's the same even if we restart Tomcat.

Thank for your help, if you have any idea...
 
Sylvain