HTTP 500 / ACLManagerService init after deployment under new Tomcat Instance

Context : 
-----------
- OS : Win XP
- JDK : 1.4.2_08
- Jahia : 4.1 build 6050
- Tomcat 5.0.28


Problem explanation : 
--------------------------------
I need to test Jahia and some portlets (webapps) under Tomcat 5.

So I've tested the migration of the Jahia application from the downloaded bundle jahia410_build6050 to a new tomcat 5.0.28 instance. 
I"ve strictly  followed all tasks explained in the the two FAQ articles 
http://www.jahia.org/jahia/Jahia/devzone/pid/454#16 and 
http://www.jahia.org/jahia/Jahia/devzone/pid/454#17.

But after booting my server, I have a HTTP 500 error due to a 
NullPointerException in the JahiaACLManagerService initialization (see the Stack trace below). I read past messages in this forum 
(http://list.jahia.org/install_list/msg01115.html and answers) but don't 
see how to solve my problem. 

So did I miss womethinf in configuration changes ? 

Thank's for help



Stack trace : 
-------------------

javax.servlet.ServletException: "Servlet.init()" pour la servlet Jahia a 
généré une exception
 
org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:670)
 
org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:637)
                 jsp.index_jsp._jspService(index_jsp.java:43)
 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

cause mère 
java.lang.NullPointerException
 
org.jahia.services.acl.JahiaACLManagerService.init(JahiaACLManagerService.java:141)
 
org.jahia.registries.ServicesRegistry.loadService(ServicesRegistry.java:684)
 org.jahia.registries.ServicesRegistry.init(ServicesRegistry.java:317)
                 org.jahia.bin.Jahia.initServicesRegistry(Jahia.java:1035)
                 org.jahia.bin.Jahia.init(Jahia.java:486)
 
org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:670)
 
org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:637)
                 jsp.index_jsp._jspService(index_jsp.java:43)
 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:802)




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