[Zope] manage_clone - Pleeeease help !!!

Hi, it's me again. :-( I have a great problem with manage_clone! If I use the following Syntax, with an explicit item to clone all works fine: <dtml-call "manage_clone(Folder.N_1, 'N_1', REQUEST)"> but, if I use a variable with the value 'N_1' like that: <dtml-call "manage_clone(Folder._['variable'], 'N_1', REQUEST)"> I don't have the permission to clone, and get a login window in order to authorize !!!! That's crazy, ... another great bug??? I am using Zope 2.2.4! What could I do ? Pleeease help if you can ! Thank you , ... Marc