[xwiki-users] Unable to display Export page

Hi, I'm runnig Wiki 4.1.3 (Ubuntu 12.04) with a wiki content migrated from Xwiki 3.1. I use postgreSQL 9.1 I'd like to create a xar backup of this migrated content so : - I connect using the Admin user - Go to wiki administration - Content -> Export ( http://localhost:8080/xwiki/bin/export/XWiki/XWikiPreferences?editor=global… ) and xwiki shows a blank page with top menu, logo and footer. The Export form is not shown and no administration menu on right. Tomcat output shows no error except : WARN o.x.v.i.DefaultVelocityEngine - Deprecated usage of getter [com.xpn.xwiki.api.Util.getArrayList] in unknown namespace@794,35 Any idea ? The import page is displayed correctly, but that's not what I want to do. Regards.