bug while restricting access

dear all, I am having trouble restricting the access of a document to my XWiki registerd users only. If i apply the edit, view rights to XWiki.XWikiAllGroup at the last document published, I get the following error message when logout : Error number 4001 in 4: Error while parsing velocity page Main.WebHome Wrapped Exception: Invocation of method 'formatDate' in class com.xpn.xwiki.api.XWiki threw exception class java.lang.NullPointerException : null While when I do the same for an older document, this document is effectively hidden when I logout but the others appear in double! Any idea? Many thanks in advance, -- Arnaud Béchet Station biologique de la Tour du Valat Le Sambuc - 13 200 Arles - France Tel : +33 (0)4 90 97 29 73 Fax : +33 (0)4 90 97 20 19 www.tourduvalat.org