Cannot create an user nor a group using the admin interface with user Admin or superadmin

I've just installed XWiki Enterprise 1.9 war on Tomcat 5.5 on debian etch using a PostgreSQL database and imported the default XE 1.9 XAR using superadmin account (deactivated now). Using either superadmin or the regular Admin user, in the admin interface and in the Users or Groups panels, the button "Add user" or "Add group" links to '#' and thus does nothing. I'm using Firefox 3.0.11 on Ubuntu Linux Jaunty Jackalope 64bits.